First steps toward having an scenario map.
HP and minions alive carry over between battles.
It doesn't seem like we are using threads soon.
Generals can be deployed with the new requisition

Many other changes other than the new requisition resource:
* Areas now use the battleground as basic variable, but can get the
general if they need some information from him.
* New teleport method for entities.
* Minions and generals got the side and (x,y) parameters order
swapped. (x,y) parameters are now optional always.
* Last change not yet applied on Entity and other subclasses. This
is so confusing right now, I think.
* render_bar() properly moved to window.py