Small improvements :
- Adds keyboard shortcuts for the magic wand
  - AcceptGrowth -> ctrl+Return
  - RemoveSeed -> ctrl+BackSpace
The shortcuts can only be activated when the magicwand is.
- Now, after interaction with the sliders/spinboxs/buttons of the
  toolbox the focus should go back to the view
- Now, when a seed is planted, a call on undo via ctrl+z will remove the
  seed.