Bug fixes, communication changes

Communication changes:
- Field, Model and GameController get the option to communicate about
  the changed fields, so it's not neccessary to update the whole map
  every time something changed
  This new communication use PropertyChangeSupport and Listener pattern

Bug fixes:
- No more ConcurrentModificationException when player shoot
- Portal can open
- Portal has its function, so it works as a portal not just a decor
- Player's shoots works as it needs to work

Smaller changes:
- Inverse direction function goes to Direction class
- Testmap improves