Co-authored-by: Hans Moog <hm@mkjc.net>

Unit test for the following:
 - MessageID methods
 - NewMessage
 - Bytes
 - FromBytes
 - MessageFromMarshalUtil
 - ForEach...

With multiple (max 8) parents, there is less space for payloads.

* Feat: Added a package for common sentinel errors

* Fix: fixed wrong import

Co-authored-by: Hans Moog <hm@mkjc.net>

* Fix: refactored Payload to have its own package

* Fix: fixed comment

* Fix: fixed wrong comment

* Fix: reverted some changes to keep the PR as small as possible

* Refactor: refactored Data to GenericDataPayload

* Fix: fixed last refactor issues

Co-authored-by: Hans Moog <hm@mkjc.net>

* Remove storageprefix package and merge with flattened database package

* Bump up database version

* Update packages/database/prefix.go

Co-authored-by: Ching-Hua (Vivian) Lin <jkrvivian@gmail.com>

Co-authored-by: Angelo Capossele <angelocapossele@gmail.com>
Co-authored-by: Ching-Hua (Vivian) Lin <jkrvivian@gmail.com>

* refactor: Move spammer and storageprefix to packages

* refactor: Import spammer and storageprefix with new path

* refactor: Move messagelayer/message to tangle/

* refactor: Modify the method receiver and annotate the error messages

* refactor: Move messagelayer/payload to tangle/

* refactor: Modify the method receiver and annotate err messages in payload

* refactor: Move messagelayer/messagerequester to tangle/

* refactor: Modify the method receiver in requester

* refactor: Move messageparser/builtinfilter to tangle/

* refactor: Move messageparser/ to tangle/

* fix: Import fmt and minor fixes

* refactor: Move messagefactory/ to tangle/

* refactor: Move tipselector/ to tangle/

* refactor: Rename method receivers in tipselector

* refactor: Move messagelayer/tangle to tangle/

* refactor: Rename method receivers and annotate error messages in tangle

* refactor: Move messagelayer/test to tangle/

* fix: Update to the develop branch

* refactor: Create data payload in testing message creation

* refactor: Use tangle package in gossip

* fix: Fix 



* fix: Rename for consistency

* fix: Move message related const from payload.go to message.go

* refactor: Use single character for method receivers

* fix: Fix the unit test by using the correct variable name

* refactor: Use tangle package in spammer

* refactor: Use tangle package in faucet

* refactor: Use tangle package in networkdelay

* refactor: Use tangle package in valuetransfer

* refactor: Use tangle package in messagelayer plugin

* refactor: Use tangle package in gossip plugin

* refactor: Use tangle package in syncbeacon plugin

* refactor: Use tangle package in syncbeaconfollower plugin

* refactor: Use tangle package in webapi plugin

* refactor: Use tangle package in issuer plugin

* refactor: Use tangle package in pow plugin

* refactor: Use tangle package in metrics plugin

* refactor: Use tangle package in drng plugin

* refactor: Use tangle package in prometheus plugin

* refactor: Use tangle package in dashboard plugin

* refactor: Use tangle package in integration tests

* fix: Fix unit tests

* refactor: Remove binary/messaglayer

* Feat: merged marshal changes

* Feat: removed superfluous test

* Fix: fixed wrong comment

* refactor: Annotate error messages in marshal functions

* refactor: Import fmt package

* refactor: Aggregate all filters into filter.go

* refactor: Rename Factory to MessageFactory to clarify the functionality

* refactor: Rename Parser to MessageParser to clarify the functionality

* refactor: Rename Requester to MessageRequester to clarify the functionality

* refactor: Rename Parse to FromMarshalUtil for naming consistency

* refactor: Fix comments

* refactor: Fix comments

* fix: Use the correct function

Co-authored-by: Hans Moog <hm@mkjc.net>

* refactor: Move messagelayer/message to tangle/

* refactor: Modify the method receiver and annotate the error messages

* refactor: Move messagelayer/payload to tangle/

* refactor: Modify the method receiver and annotate err messages in payload

* refactor: Move messagelayer/messagerequester to tangle/

* refactor: Modify the method receiver in requester

* refactor: Move messageparser/builtinfilter to tangle/

* refactor: Move messageparser/ to tangle/

* fix: Import fmt and minor fixes

* refactor: Move messagefactory/ to tangle/

* refactor: Move tipselector/ to tangle/

* refactor: Rename method receivers in tipselector

* refactor: Move messagelayer/tangle to tangle/

* refactor: Rename method receivers and annotate error messages in tangle

* refactor: Move messagelayer/test to tangle/

* fix: Update to the develop branch

* refactor: Create data payload in testing message creation

* fix: Fix 



* fix: Rename for consistency

* fix: Move message related const from payload.go to message.go

* refactor: Use single character for method receivers

* fix: Fix the unit test by using the correct variable name

* Feat: merged marshal changes

* Feat: removed superfluous test

* Fix: fixed wrong comment

* refactor: Annotate error messages in marshal functions

* refactor: Import fmt package

* refactor: Aggregate all filters into filter.go

* refactor: Rename Factory to MessageFactory to clarify the functionality

* refactor: Rename Parser to MessageParser to clarify the functionality

* refactor: Rename Requester to MessageRequester to clarify the functionality

* refactor: Rename Parse to FromMarshalUtil for naming consistency

* refactor: Fix comments

Co-authored-by: Hans Moog <hm@mkjc.net>