[ktest] simplification and refactoring

I finally made the changes that I had in mind for a while.

* Instead individually passing settings, `KTestOptions` object is passed between classes. This became a problem after we had more and more global settings.
* I removed string constants. Since they can't be used in annotations, most of them were left unused after moving to JCommander. For uniformity I removed the rest.
* Some various unused stuff removed.
* Injected `KExceptionManager` is used instead of the one from `GlobalSettings`.

Just to make sure I'll run test suite on Windows manually.
It's deprecated in the sense that we want to get away from it, but not in the sense that references to it should be removed blindly. Currently it should be continued to be used in places where dependency injection is not available yet.