Remove ClassReferenceNode.
Add String>>capitalized and isCapitalized.
Merge branch 'master' of github.com:amber-smalltalk/amber into class-ast-node

Conflicts:
	st/Compiler-Tests.st
Refactored String>>capitalized.
Merge pull request #652 from matthias-springer/class-ast-node

Remove ClassReferenceNode, allow capital letter variables