Add MercatorTiledImageLayer support.

[EMaksymenko]

Description of the Change

Added MercatorTiledImageLayer and its related components to easily connect popular tile sources such as OpenStreetMap, Google etc.

Why Should This Be In Core?

Extends the general usefulness of the SDK.

Benefits

Adds the capability to use maps and imagery provided in the Mercator projection.

Potential Drawbacks

Re-projected tiles are not cached in a persistent cache, because Android SDK has no sdcard cache yet. Re-projection is very resource intensive in low-end devices.