This introduces new functions to Profile for querying starred review

request and group information in a way that leverages a cache. The

following functions have been added:

get_starred_review_groups_count()
get_starred_review_requests_count()
has_starred_review_groups()
has_starred_review_requests()
is_review_group_starred()
is_review_request_starred()

Both get_starred_review_groups_count() and

get_starred_review_requests_count() return the number of starred

groups/review requests for a given user and optional LocalSite. These

values are cached, making subsequent lookups fast, and enabling

decisions to be made based on the content.
These are wrapped by has_starred_review_groups() and

has_starred_review_requests(), which fetch the count and return whether

there's at least 1 item.
is_review_group_starred() and is_review_request_starred() return

whether a given review group or review request are starred. This queries

the database as normal, but if the user hasn't starred any items of the

given type, this won't perform a query at all.
The star/unstar methods will invalidate the cache count.
Most users don't star items, and likely don't star them very often. By

caching, we can avoid a lot of lookups and simplify database queries for

users (which will be implemented in another change).

Unit tests pass.