Implement repeaters for keyCapture events

This is really just a playful PR - but it might be handy at some point, as it's very simple, yet effective.

Just like state is doing it know for his keyCapture events, that move through tokens, one can wrap the callback function of a keyPress event in a call to `keyCapture.doRepeated`. The keyCapture service is now listening to numeric input and knows how to resolve it properly.

Let's say I have `w` configured to jump to the next token. It's possible to type `12w` to jump 12 positions ahead.

Fixes some bugs in arethusaUtil and state in the process.


PS: I am absolutely sure that the sheer existence of this PR has nothing to do with the fact that I am a vim user ;)