Remove proxy from most default imagery providers.

ESRI and OpenStreetMap (OSM, Stamen, and MapQuest) all now support CORS headers directly.

Also remove `FeatureDetection.supportsCrossOriginImagery` and related checks which only applied to old WebKit versions (Safari before version 6).
Remove unused modules.
Merge pull request #1520 from AnalyticalGraphicsInc/removeProxyFromImagery

Remove proxy from most default imagery providers.