UI refactored Map View, closes #133

 * converted MapView to use Marionette.Views.LayoutView and split parts in subview managed by regions
 * leaflet map objects are load through GeoJSON and bound to Ns.collections.Geo
 * loading speed improvements: essential JSON data is preloaded
 * django-leaflet settings are used for map generation
 * all the javascript objects are now stored in a single global object named "Ns" (which stands for Nodeshot)
 * fixed #171 (UI: show layers / statuses clash)
 * addressed also #169, but user feedback needed
 * a free satellite tile layer is now included by default
 * base layers (tiles) are managed from the map toolbar
 * map popup permalink
 * add node permalink
 * automated UI tests with selenium