Make window resizable

If the window is not resizable then the program doesn't work on a
multi-monitor XMonad setup. I didn't investigate the issue more closely
but this change seems to fix it. However I think that there's a better
way.
Fix naming and add some comments
Add penalty delay when typing during a break
Fix whitespace
Tick the timer every second

The concept of modes is introduced. Additionally the timer ticks every
second. This will help us to detect work pauses in the next version.
Set the initial work duration