Revised and improved Xbase's formatter and moved it to Xtext.

TODO:
- disallow overriding non-whitespace
- hook up serializer
- update JavaDoc
- move comment tests from Xtend to Xtext

Change-Id: I7d31999f43888ce2492502be6871e88c0532ecb9
add xtext.ide to ui feature

Change-Id: I0d96c70263475baaeeec74c56b367e913285a6fc