Switch breakpoints system to model/view separation
- this was relatively easy, because it was in a round-about way already being stored as such
- BreakpointController used to just deal with editor marks, now it is the model and repository for breakpoints
- for some reason, setting a title on the first column makes the header disappear (..??!!)

I love model/view, it helps to delete heaps of potentially buggy code :)

Still todo for breakpoints: more testing, re-integrate tracepoint editor

Also a few miscellaneous code cleanups and small fixes