Improve performance of search when the query is in the cache.
Speed up in the search cache by avoiding construction of the set of all book ids when the cache hits

Merge branch 'master' of https://github.com/cbhaley/calibre
Tentative implementation of using global render cache when evaluating composite columns in composite_getter()
Refactor to make the template rendering logic its own function
...
...
...
Make render_composite() an internal API
...
Improve performance of get_categoris by using ProxyMetadata objects