Added unit test for issue #267
added missing linker flags for unit test target
Moved interpretation of tag attributes into new method interpretAttributes.
This should be called after inheritAttributesFromElement: because this also copies/inherits the paragraph style.
So far interpretAttributes deals with Apple-converted-space and writing direction.
containsAppleConvertedSpace is now also inherited from super element
Fixes #267
Removed deprecated ivar _tagContentInvisible
The functionality of this is now shared between displayStyleNone and the specialized DTHTMLElement subclasses for ignoring tag contents.