Updated Area class

Suppressed applyEffectOn() method -> the game does it now.
Updated Entity class

Added the possibility to manipulate directly the center position of the
entity. Also updated toString method.
Updated StaticEntity class.

Added Effect feature:
	A staticEntity has know a passive effect and an effect radius (the area
	that defines the entities affected is a circle). Constructor has been
	updated and method (for Effect management) added.
Added the use of center positioning.
Updated Game class

The play()  method handles the interaction between staticEntities : the
application of effects.
Updated

Added constructor to manage name personalization. 

WARNING : Changed the way the position of a StaticEntity is set:
We do not use the top left corner anymore : we use the central position.

This do not apply for Areas.

The previous system is still usable (setOrigin()).
Updated Main class

Added names to the trees to ease the comprehension of the tests. Added a
tree to the game to observe the interactions between StaticEntities.
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/fr/iutvalence/java/mp/wim/model/Area.java