MobileMapStarter update: Tile caching and Chrome compatibility

Yesterday I put the finishing touches onto a major revision of MobileMapStarter.

- The previous version used imgcache.js to passively cache map tiles as you browse. The new version uses a new system, allowing you to download a specific area for offline use. No more panning and zooming repeatedly -- just zoom out, center it, and hit Download. It even has a nice status thingy, and skips over tiles that you already have.

- I spent a lot of time getting the caching to work in Chrome too, so you should be able to prototype your app on the desktop.

- There were also some other minor things: typos, minor adjustments, and changing out the Streets basemap for the Mapbox Satellite basemap.

Go git it!
https://github.com/gregallensworth/MobileMapStarter/