Review Board 5 introduced some mechanisms for optimizing queries to

avoid filering by Local Sites if there aren't any Local Sites in the

database. We updated a few queries to use this, but not all.
This change updates ReviewManager to take advantage of this, reducing

the complexity of queries and helping the database better use its

indexes on a typical install.
There's also a fix for building queries for Local Sites, taking

advantage of the field name provided.
This is the first in a series of changes for optimizing Local Site

filters out of queries.

All unit tests pass.