Map visualization

 - upgrade some gems
 - add profile env to trace performance issues
 - add `/geo_data/tile/:zoom/:x/:y` and `/maps/:id/tile/:zoom/:x/:y` to get data that intersects a given tile
 - add some scopes to geo_data:
   - deselect: selects all columns except the listed as argument
   - with_geojson: gets the geometry as geojson directly from PostGIS as field_geometry
   - tile: gets the entries that intersects the given tile
   - as_geojson: converts to feature collection
 - implement the map visualization of geo data collections
 - some fixes
 - refactor
 - specs