implement phobos for upbge fork (clone repo) - help wrap BT_MultiBody in upbge/bge fork of blender. #290

1. We currently do not have the physics type 'multibody' in upbge - the game engine development fork of blender

Help us wrap BT_Multibody using pieces of the already existing pybullet code to generate multibody agents.

Additional context
Currently we can export a URDF from blender to pybullet
upbge is a game engine layer restored to blender that was removed (BGE) now using eevee and modifiers / bpy in realtime.
having multibody agents could allow for animations to be recorded and then played back later in cycles / rendered offline*
(so proxy rigs / gameplay can make movies)

• robot in upbge using ik/ armatures https://www.youtube.com/watch?v=fMwe9hGZb9w

• record gameplay as f-curves - https://blenderartists.org/t/blender-upbge-as-a-animation-tool-recording-keyframes-physics-agents/1235434/7?u=blueprintrandom

upbge.org/#/