refactoring: implements per account contacts, trust requests & more

- seperates contacts by account
- implements the trust request API
- introduces localization strings and transifex update mechanism
- adds lodepng to remove windows photobooth png metadata
- changes icons
- adds default colored initial avatars
- changes logo images
- complete overhaul on the ui/ux

Change-Id: I43914ff63a48bb43a6997721773df5029a1650b5