Allow searching for games based on some criteria

[AarjavP]

Currently the api just returns all games, there is no filtering or searching for them. This issue is mainly to setup the mechanism to do the filtering/searching with. The things we can search by will likely change over time.
To start with I think we want to support searching by category, number of players, type/tags.

We may also need to have some listing for categories. Will be made clearer after the mock ui / use cases are more fleshed out.