Add overlays with Deprivation data

Adds two new layers showing information from the English Indices of
Deprivation [1] at the Lower Level Super Output Areas (LSOA) level, from
the Department for Communities and Local Government. Boundaries are from [2].

Boundaries are loaded from TopoJSON.

[1]
https://www.gov.uk/government/publications/english-indices-of-deprivation-2010
[2] https://www.sharegeo.ac.uk/handle/10672/320
Merge branch 'master' into gh-pages