Box2DBody fixes and optimizations

* Inlined all getters for properties that are never changed dynamically
  by Box2D to return the value from the b2BodyDef.

* Fixed the value of the 'awake' property, which was always returning
  the value in the b2BodyDef because of a missing 'return' keyword
  for the case where the body was created.

* Changed type of linearDamping, angularDamping and angularVelocity to
  'float' to match the Box2D variable they are stored in.

* Fixed Box2DBody::angularVelocity to return the dynamic value when
  appropriate, which might have changed from the b2BodyDef value.

* Fixed Box2DBody::setAngularVelocity to not compare the degree variable
  with the radian variable.

* Don't do a qFuzzyCompare in Box2DBody::setGravityScale. There is no
  reason why the gravity scale shouldn't match exactly.
Fixed conversion of mass

Mass is per square meter so the scale ratio should be squared as well.