Box2d - Misc initializations - Complete b2WorldManifold Initialization

The main commit is the b2WorldManifold initialization completion.  This fixed a couple of issues but still does not fix the main Debug.Assert that the commit states.  Still getting that for some reason.

Added epsilon squared to the b2Settings.  This is being run through quite a few times so this would take out an extra multiply as it is already computed.  Nothing big but still.