Implement saveState/restoreState for deformable objects

[danielpmorton]

This will serialize the deformable object upon a call to saveState, and then deserialize the deformable object's node properties upon a call to restoreState. Previously, every object except for deformables would be saved/reset, when using RESET_USE_DEFORMABLE_WORLD

The code style here is based on what I've seen in the repo already. I can make more changes as needed too

I also wanted to check to see if I should restore more of the node attributes from the serialized data - for instance, m_pad, m_material, m_inverseMass, m_area, and m_attach. The current attributes I'm restoring seem to work well, so it remains unknown if also restoring these other properties will lead to any improvements