UI for making users location_authorized_users

[barankyle]

Currently, the only way to give someone authorization to access a location is to invite them. There should be a UI that allows location_admins to directly make location_authorized_users (or instance_authorized_users), so that they don't have to be in that location and send an invite.

Stretch goal: allow location_admins to remove location_authorized_users. Possibly also remove authorized_users' ability to invite anyone, and make it so only location_admins can invite people.