UI: Ns.views.map.Add not instanziated if not authenticated
UI: cached map data gets refreshed in the background
UI: removed obsolete Ns.preferences object
UI: node details view stores coordinates

(preparation for #203)
UI: avoid refreshing map data at each map hit

Refreshing the map data on each map view is expensive both from a server
point of view and from a client point of view (browser becomes less
responsive while fetching thousands of backbone models).
Better refresh the map data on key events only, we begin with login and
logout events.
UI: optimized toggleLayerData() in Ns.views.map.Content
UI: enlarged width of step1 and 2 of "add node"