ByteCodeAnalyzer: update license

Based on mvn license:update-file-header results.
Create WelcomeService

Created a new WelcomeSerivce (a port and refactoring of the ImageJ2
ReadmeService).

This service, on display of a UI, determines if it's the first time the
current app has run. If so, a welcome message is shown, and a
WelcomeEvent is published for other interested parties to consume.