Add Share Users Access Cache Table and Triggers for Performance Improvement

This 4.6.x commit made it in. I can revert it if you think this needs to stay as is (adb4dc23d), but that's what we're on in 4.6.x:
https://github.com/xtuple/xtuple/commit/84e5eba947cd7c97cf183fe46547b97c38678a6e