Multiple fixes for loading external objects

[gergondet]

This PR addresses the issues raised in #39:

• Static objects can now be loaded as external objects
• Composite objects can now be loaded as external objects
• Extra modules can be loaded from the user folder instead of the global installation folder

For now we still don't allow a mismatch between the kinematic structure in mc_rtc and the kinematic structure in the corresponding MuJoCo model, this would require a little extra work to handle the gaps in qpos/qvel

[rohanpsingh]

Does this address additional objects that have multiple joints? (say one floating base and some hinge joints)

[gergondet]

Hi @rohanpsingh

Does this address additional objects that have multiple joints? (say one floating base and some hinge joints)

Yes. Here's an example where the only things loaded via mc_rtc are the standing JVRC1 robot and the ground:

Other than that:

• the box is free object with no joint other than the free joint
• the checkboard things are fixed deformable objects (the same as linked by @mmurooka)
• the robot is a non controlled JVRC1 loaded

[rohanpsingh]

Awesome!