WL-3116 Get an up-to-date list of locations

When adding a new meeting, the SignupMeetingsBean can still exist but might
not have updated the flags for existance of categories or locations.

The recent patch (#27) for WL-2926 causes the locations and categories to be
cached, so we can just call the local methods `getAllLocations()` etc.

:wrench: It's worth merging #27 before looking at this one.