[WIP] Allow atom selection via VR controllers

[Nargaruga]

This allows the user to select atoms by pointing the laser and pressing the button mapped to Action1 (typically the trigger), as requested in #378.

Some problems are still present:

• there is a considerable offset between the laser pointer and the atom that is actually selected. Reducing cRange in layer1/ScenePicking.cpp does not seem to improve the situation by much.

Possible improvements:

• add the ability to select whole residues;
• change the laser color when a residue is being pointed at (similar to how the laser becomes blue when aiming at the menu).

Additional notes:

• this requires openvr_cut_laser to be set to true in layer1/SettingInfo.h;
• I was not able to compile PyMOL with OpenVR until I added the #include <thread> to contrib/vr/OpenVRControllerModel.cpp (change not included in the commit). Not sure if it's a configuration issue on my end.