Added first partial support for Tiled Ellipse object (WIP)

- Ellipse will be automatically converted to a corresponding bounding
box rectangle
- (debug) drawing to be fixed
- Position is off (probably due ellipse coordinates system)
Store the center position of the circle (although Tiled seems to provide the top-left origin point)

This is also more inline with what chipmunk is doing
Set default origin of shape objects to `0,0`, as they are offset position compared to the entity (body)

NOTE : this is void by the current hack (that set collisionBox to
shape[0] and then re-assign the collisionBox pos vector to the entity
reference one)
Fixed debug drawing of the ellipse
DebugPanel : Translate the shape before drawing it, since it's an offset compared to the entity (body)
doc : fixed private properties being displayed as global !
WIP : Added partial support (through a BB) for PolyShape object

Object position, and corresponding shape & bounding box are not correct
(the BB is however correctly set around the polygon)
Fixed the `getBounds()` function (thanks Jay)

also fixed the mixed tabs & spaces, because after all .... I'm not such
a bad person :P
(temporarly) added a SlimeEntity in a polygon shape to ease testing the feature
fixed `points` being redeclared
Merging with master branch