[2.0] Fixed several referential integrity issues. Fixed critical issue with inserts being run twice on postgresql/oracle. Added support for additional tree walkers that modify the AST prior to SQL construction and started to play with it in a testcase.

DQL Parser work. Getting some first tests back running. Reorganizing all parser rules into the Parser itself.

Fixed paths that were referring wrong namespace resolution.
Implemented more Parser and AST classes: JoinVariableDeclaration and Join.
Fixed wrong semantical checks of IndexBy grammar rule. They should be in IdentificationVariableDeclaration and JoinVariableDeclaration.

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.