Change the way we draw markings of speeling errors. Instead of using the qt way we draw it ourselves.
This has the following benefits:
- we don't have to relayout after finding spelling errors
- we can have more than one type of marking (spelling, grammar, etc)

This commit also changes the way we ask for spellchecking to be performed. The old way had some
shortcommings that could lead to text not being checked at all