Update licenses, add credits section in app

[TheZ3ro]

This PR:

• Remove AdbViewModel.java credits since @rocodes rewrote it in Refactor: state-aware ViewModel and app flow  #37
• Remove "BSD" and "MIT" licenses since they are not relevant anymore
• Added credits to our translators in the COPYING file. Apparently the URL with credits can be seen only after authentication. I need to investigate if there is a Public alternative.
• Added credits in app:
  For now:
  • in the credits list there's only us maintainers but we can insert there collaborators for Pull Requests and translators.
  • it is placed in the "About Us" section but we can discuss where to move it.

[lsd-cat]

Tested it and it looks great! I would cut a bit the Osservatorio description, maybe just keep the first paragraph? What do you think?

[TheZ3ro]

sure! I'm open to any change. will push an update later if you don't do it before me