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.

Finished first parts of SELECT support. Two test cases added and passing. Introduced the concept of DCTRN in queryComponent. Added concept of queryField, which validates for already defined fields in SELECT.