Exposure export

This branch includes several things:
- Integration fo the Leaflet application into the OpenQuake Platform
- Integration of the GRUP population tileset base layer into the application. 
- The dwelling fractions interactive app; select a dwelling fraction layer, and then hover the mouse to view pie charts of the dwelling fractions. One layer for Admin level 0, and another layer for Admin level 1 (only for Portugal).
- The Exposure Export tool; zoom in, activate the selection tool, pull a selection box over the map, download csv and or nrml file. The download will stream the results.
- A Django application that connects to an external database.
- Tool tip; the tool tip is a popup on the UI to provide the user with information of how to use the tool(s).
- Update the installation script to include the above applications with the option for the user to install the exposure tool. The installation script requires the dataabse connection parameters.   

A few notes: 
Once installed, view the applications under: View - Basic Datasets - Exposure Gridded Data
The iframe of the application is not set correctly to 100%.
The exposure export tool has may options for the selection of the dwelling fractionshard coded, this will be expanded in future versions.
Currently the dwelling fractions application, and the exposure export tool and the GRUMP tileset are all in one application, this may be brocken into several individual applications in the future, but has not been defined yet.