Fixed hasModifierProperty(String) to support '@:final' and 'abstract' prefixes on class declaration.
Fixed getModifierList() to reasonable extent and commented it out, for completion during refactoring actions' implementation.
Some optimizations in if/return statement expressions.

Only pending in AbstractHaxePsiClass is to fix underlying HaxePsiReferenceList to overcome the class-cast conflict with JavaCodePsiReferenceElement[]
Missed including these in earlier commit.