[Android] Fix ScreenOrientation's package missing issue when integration with Cordova.

Because the ScreenOrientation API is in the ".../api/screen_orientation"
folder, but it's packaged as ".../api/screenorientation/...".

Move the ScreenOrientation implementation from "screen_orientation" folder
to "screenorientation" folder.
Merge pull request #1514 from junmin-zhu/screen

[Android] Fix ScreenOrientation's package missing issue when integration with Cordova.