Cleaned up tests regarding indexed properties.
Improved support for indexed properties.

More types and types with different qualifiers are supported now - in both backends. See test cases for details.
Fixed the getter/setter to property passes to not include synthesized methods.
Removed obsolete code.
Added extension method SetPropertyAsReadOnly to ASTContext.

The Property.HasGetter and HasSetter method will take the GenerationKind flag of the field/method pair into account.
Merge pull request #233 from azeno/property-improvements

Improved support for indexed properties