Entirely new caching system. Chrome compatibility.

- Removed ImgCache (passive caching of visited tiles) in favor of an
active cache-seeding approach, and an explicit "Use offline cache"
checkbox. Handles both Cordova and Chrome, for easier prototyping.
- Improved various other behaviors when using Chrome, aiming to be able
to prototype effectively in Chrome.
- Added a working example of the geocoder.
- Changed the default layer options: Mapbox Terrain and Mapbox Satellite
- Merged config.js into map.js
- Corrected a typo in config.xml