Origin/ai

Depends on the merge of origin/AI in engine and common

-Steering Behaviors class added
-Path class -- Used by one of the steering behavior functions to do the object follow the path.
-IFollowPath class -- implement the methods needed to follow the path
-Changes in the physics simulation. In the end of update the force is reset to 0. All the forces inserted by events are stored in the tick_force variable and applied in the next update.
-Inserted a macro in Game.h - getObject(handle) : *BaseObject (receive a handle and return a pointer to its BaseObject)