Add better support for expressions & improve tests
Reject expression test

removed on test as it was redundant, everything and more was tested in WebservicesSubsystemParserTest.java
[AS7-6128m] Adjust model representation of COLUMN_NAME and COLUMN_TYPE to support expressions.
[AS7-6128m] Centralise transformer code.
[AS7-6128m] Add reject expressions transformer test case.
Make it possible to have fine-graind validation for complex attributes