IE, logging, and geolocation

Contains changes in the appcache branch, so #15 should be evaluated/merged first.

For IE versions < 10, we need aight.js to fill in some functionality.

Silence our console output by default but let us choose a level of output for debugging. We should still avoid logging objects, since that is a memory leak.

If our geolocation accuracy is poor, we should avoid drawing a gigantic circle over the map.

Use high accuracy geolocation, since otherwise we might rely on wifi/cell location, which is not great for this purpose.

When panning for "Locate Me" functionality, try to avoid throwing off the user's sense of what's going on with the map. If they've zoomed out manually, then zooming in automatically could confuse them. This will probably require some more user testing to get just right.

/cc @hampelm