Add a 'q' parameter for filtering tile data

The q parameter is converted from OTM2 JSON to a SQL
select statement that is compatible with windshaft/grainstore.

I pushed hardcoded values out to config.json so they can be easily changed
or replaced via templating during deployment.
Merge pull request #5 from jwalgran/topic/filter-tiles

Add a 'q' parameter for filtering tile data