Merge pull request #44 from bjorn/master

Box2DWorld improvements, additions and optimizations
Small changes to Box2DDebugDraw for consistency
Added Body.applyAngularImpulse
Added Body.addFixture

Allows dynamically adding fixtures, for example in
Component.onCompleted.
Check whether body is created in two Box2DBody methods

Otherwise calling these methods on the wrong moment would crash.
Simplified synchronization code

Rely on synchronizing the position and angle of the b2BodyDef to avoid
doing unnecessary conversions and to make the checking of changed
values accurate, removing the need for qFuzzyCompare.