Start refactoring codebase to use new message layout - WIP

dapps/valuetransfers/packages/payload/payload_test.go

packages/tangle/message.go

packages/tangle/message_test.go

packages/tangle/messagefactory.go

packages/tangle/messagefactory_test.go

packages/tangle/payload_test.go

packages/tangle/tangle.go

packages/tangle/tangle_test.go

packages/tangle/test_utils.go

packages/tangle/tipselector.go

plugins/dashboard/explorer_routes.go

plugins/dashboard/visualizer.go

plugins/webapi/message/findById.go

plugins/webapi/tools/message/pastcone.go