Geofiltering

Add a URL query param "inoxford"; first implementation should use a geofilter to filter from a point for a given radial distance (both stored in configuration). Might need to be revisited later to be computed at indexation time.

https://cwiki.apache.org/confluence/display/solr/Spatial+Search
Maybe just document this? as it's valid to have query string param with no value. This way we can say the inclusion of the paramater == true?