Implement climate overlay sliders from wireframes

[ajrobbins]

We've ingested monthly mean temperature and precipitation rasters for analysis in BiG CZ, and will be tiling them for visualization in #1976. This card is to wire up a slider that accompanies the new Temperature and Precipitation overlays in the layer selector. Each overlay actually has 12 overlays for display, one for each month. The slider enables the user to toggle between months, changing the overlay displayed.

See: https://marvelapp.com/5a66caa/screen/29342973

(slides 15-16)

[rajadain]

Depends on #1976

[mmcfarland]

Tiles are available via the azavea data-hub tile endpoint:

Precipitation
https://{s}.tiles.azavea.com/climate/ppt_{month}/{z}/{x}/{y}.png

Temperature
https://{s}.tiles.azavea.com/climate/tmean_{month}/{z}/{x}/{y}.png

{month} is a two digit, zero padded number 01-12.