Icebox Geonode2 integration

The goal of this pull request is to implement the workflow described here https://blueprints.launchpad.net/oq-platform/+spec/icebox-geonoe

The gist is to automate the generation of geoserver (and geonode) layers from calculation outputs. In order to do this we implemented the following workflow:

1) setup a geoserver style for each oq-engine output type (at bootstrap time)
2) create a SQL view for each calculation output (upon calculation completion)
3) publish such SQL view with geoserver
4) create the corresponding geonode layer
5) create a geonode map, holding all the geonode layers

Moreover, we refactored the Calculate Tab UI as now all the visualization part is managed by Geonode. I have used Backbone and Twitter Bootstrap to draw a simple UI to manage outputs and calculations