I started my "let's split all the tests into tinier pieces" adventure by writing more tests for the replace mode. The final result is this patch, that contains:

- More tests.
- Fixed a crash: when you typed Ctrl-E (or Ctrl-Y) in an empty document, it crashed. This is because in the first if statement of the commandInsertFromLine function, it should be >= instead of > (such a classic fix :P).
- Fixed a crash: when you typed Ctrl-E (or Ctrl-Y) and the cursor was at the end of the line, it crashed. This was fixed by calling doc()->insertText() for this case. Moreover, I took the chance to clean up the commandInsertFromLine function a bit. Most notably, instead of calling the cumbersome getCharAtVirtualColumn function now it will call the doc()->characterAt() function.
- I took the chance to clean up the whole KateViReplaceMode class (probably it should've been in another patch, sorry about that :P).

I started by adding more tests to the ReplaceModeTest but I finally decided to split this function into three different functions:

- ReplaceBasicTests: for basic replace actions, moving the cursor with the Ctrl key, etc.
- ReplaceUndoTests: for actions that want to undo a replacement (e.g. the backspace key). Notice the TODO's here: I'll (hopefully :P) provide another patch in the future to support the Ctrl-W and the Ctrl-U actions. Right now I'm marking this as a TODO.
- ReplaceInsertFromLineTests: for the Ctrl-Y and the Ctrl-E actions.

All the tests are passing.