getUsersWithConfluenceAccess() is very slow

getUsersWithConfluenceAccess() is pure evil. With any reasonably-sized userbase, It grinds even the most helpful server to a halt.

Currently it's called from three or four different places:

1) License check
2) Adding a new user
3) Whenever the license check cache expires

We should find alternatives, and ensure that the method is never called for anything but the license check when:

1) External user management is enabled
2) select count(*) from users > 1000

We should also just disable the license check entirely for unlimited-user licenses (i.e. 10,000 user licenses or more). Right now this limits our ability to offer licensing schemes >10,000 users per license, but tough, this is hurting us now.