Set armature for hinges

[surgura]

Hinges currently have no armature set(motor has 0 intertia itself). This is actually not realistic and can cause unstable simulations and vibrating behaviour.

Also look at servo damping(internal friction). Not as important.
And mujoco's 'forcerange', which it does not pick up from the URDF file and we have to manually set. Also not that important.

[surgura]

@tckarenchiang We should pick this up as the next issue when you have time. This is important for students.

[oliverweissl]

Adding armature helped a lot! This should definitely be added.

[surgura]

Done for mujoco. Moving to isaac gym tracker. We will not solve it for isaac right now.