Fix various spellcheck/highlighting issues:

- Decouple quote highlighting from spell highlighting, now quote highlighting works again when spellchecking is disabled.

Unfortunately, this is a bit hacky, as the methods from KTextEdit could not be reused, because they weren't virtual. KMeditor hides spellcheck-related methods inherited from KTextEdit and implements its own, properly working ones.

- Move more spellcheck code into KMeditor
- Many bugfixes related to spelling
- In KMail, sync languages used for spelling correctly between the highlighter, the config dialog and the spell dialog. This needs kdelibs 4.0.67 to work properly.

Also, spell checking in HTML mode now works, but again, you need an updated kdelibs.