Started refactoring in DQL parser to separate Production into Parser and AST classes.
Finished first tests. Currently only 4 are active in IdentifierRecognitionTest, and only 2 are passing.

Added getters to AST. Removed Production::__call. Added visitor support to AST. (guilherme: dont shoot me yet :-). visitor support doesnt hurt even if we do not use it for SQL generation). Lots of other things.