Fixed Mouse Button State Issues

Buttons would cancel each others ButtonState.Pressed  out, as well
rotating the mousewheel would cancel all ButtonState.Pressed
Added support for bypassing the content pipeline in MGCB
Expose PathHelper to MGCB and use its path normalization instead.
Renamed all GamePad files to include platform identifiers.
Moved all GamePad code to Input folder.
Added common GamePad class.
Added vibration support to GamePad under XInput.
Fixed web platform to support platform partial methods.
Added copyright header.
Fixed WinPhone platform to support platform partial methods.
Fixed Android platform to support platform partial methods.
Fixed Ouya platform to support platform partial methods.
Fixed PSM platform to support platform partial methods.
Fixed iOS platform to support platform partial methods.
Renamed GamePadState.InitializedState to Default.
Fixed some syntax errors.
Fixed syntax error.
Changed some internals to public.
Fixed some privates to internal.
Removed some unused statics.
Fixed syntax error.
Fixed some more syntax errors.
Removed stray unused SoundEffectReader class.