User location

- Add postgis

need to recreate the DB.. see new db settings on `database.yaml.sample`

- add location column to user

- GeoJSON module: 

```
GeoJSON::encode user.location
GeoJSON::encode user.location, user.id, user.geojson_properties

GeoJSON.parse geojson  # => RGeo object
GeoJSON.parse geojson, :to => :wkt  # output WKT string
```

- Geometry 

```
class MyModel
   include Geometry

  geojson_field :location  # adds location_geojson method, and handle factories

  def geojson_properties # to define feature properties on the geojson
    {:name => name, :image => "url" }
  end
end
```

- Improves overlay component:

```
<div data-components="overlay" data-overlay="<%= {:style => "dark", :message => t('some.message') } %>"
# created a dark overlay with a centered message
```

- Show user location on users#show