This is something that was mentioned by @Daniel Salazar (zanqdo) in the #animation-module chat, and I already had the code for it in CloudRig, and the mood struck to contribute, so here goes!
Normally when using Rigify, the generation target rig must be completely visible, or the generation will fail.
This patch adds a utility class which can be instanced to make sure that an object is visible no matter what.
Still, if for any reason we fail to make the rig visible, throw a useful error message, and abort generation early, before the rig is destroyed.
