Don't rotate 2D in DynamicObjectView

When switching between scene modes in DynamicObjectView, the camera offset is maintained across modes.  Several people have been confused by this behavior in 2D, since it rotated the map.  This change eliminates the 2D rotation but maintains everything else.

See: https://groups.google.com/d/msg/cesium-dev/BEagEreTQ6A/aAfULgveI1oJ for a recent example.
Merge pull request #995 from AnalyticalGraphicsInc/2d-no-rotate

Don't rotate 2D in DynamicObjectView