Add tile colors for common spatial file formats

[phargogh]

CKAN has the ability (through some custom CSS) to add tile colors for whatever extensions we want. It turns out that the extensions we commonly work with (*.tif, *.shp, etc.) don't already have colors predefined. It'd be nice to add some.

https://github.com/ckan/ckan/blob/b7204bb307abb1f488b5d409262db40b1e840d59/ckan/public/base/less/dataset.less#L174