Fixed up the WeldJoint

* Don't crash when initialized before creation
* Separated defaulting for localAnchorA, localAnchorB and referenceAngle
Fixed up the WheelJoint

* Don't crash when initialized before creation
* Separated defaulting for localAnchorA, localAnchorB and localAxisA
* Added inverting of Y axis for localAxisA and normalized it, since
  non-normalized values were doing strange things.