Adding YUVImage and YUVCanvas.

YUVImage is a container class to hold YUV data and provide
various utilities, e.g. to set/get pixel values for different
YUV formats, fast copying routines, etc.
Currently supported YUV420 Planar and YUV420 Semi Planar.

YUVCanvas holds a reference to a YUVImage on which it can do various
drawing operations.

Change-Id: I052a57b7fbc834efe1626914f76c04c091996cac