Feat: Added Signature checks for value transfers to MessageParser (#471)

* Feat: Added Signature checks for value transfers to MessageParser

* Refactor: renamed to SignatureFilter

* Update dapps/valuetransfers/packages/tangle/signature_filter.go

Co-authored-by: Angelo Capossele <angelocapossele@gmail.com>

* Update dapps/valuetransfers/packages/tangle/signature_filter.go

Co-authored-by: Angelo Capossele <angelocapossele@gmail.com>

* Refactor: refactored code according to guard programming style

* Refactor: refactored some code

* Refactor: refactored code + adjusted go import settings

* Refactor: changed goimport of value dapp

* Refactor: refactored some more code

* Feat: more refactor :D

* Refactor: simplified constructor

* Refactor: reordered properties of struct

* Refactor: test

* Fix: fixed bug in payload parser (fallback to generic)

* Refactor: adjusted comment

* Fix: fixed conditions for third test case

* Refactor: refactored comment

Co-authored-by: Hans Moog <hm@mkjc.net>
Co-authored-by: Angelo Capossele <angelocapossele@gmail.com>