URDF parsing

[thowell]

Add functionality for parsing values:

• joint limits
• damping
• friction (?)

from URDF models, instead of adding post hoc in an environment.

[janbruedigam]

Parsing of damping is included now

[simon-lc]

we could add joint friction to URDF parsing when this feature will be added to Dojo.
Also I was thinking, maybe we could parse 'collisions' so that contact is modeled in the URDF
A collision holds the contact shape (sphere, capsule, box, half-space) its position/orientation wrt the object it is attached to, the friction coefficient