Configure tilestache

[dwins]

Tilestache has a number of configuration parameters which will all affect the performance and scalability of the final deployment. We should consider this carefully. I think that the final set of layers we will want to expose will be:

1. osm baselayer (PNG)
2. building footprints (PNG)
3. solar efficiency raster (JPG)
4. solar suitability raster (JPG)
5. building footprints (utfgrid)

If we can coalesce some of these (perhaps we never need to show solar efficiency without also showing suitability) then that is desirable. The underlying data shouldn't be changing often so we can probably get away with a very long maximum age for cached tiles.