cervisia's resolve dialog

I'm currently working on the resolve dialog in Cervisia. It has some bug reports (see bug #74903 and bug #46871) that are not easy to fix in a sane manner without changing the design. The main problem is the handling of the new line markers, especially at the end of the file.

The redesign will hopefully fix the above bugs and make the source code more readable. Unfortunately I'm not sure if this will be "back-portable" to the stable branch without some testing and the next minor release is near.