Common: Added CameraMetadata -> libexif converter

A fully-ported version of the ExifUtils class from
ChromeOS (see [chromeos]/src/platform/arc-camera/common/exif_utils.cc)

 * Made into an interface to remove libexif dependencies
   from header file
 * Rewrote ChromeOS dependencies
 * Minor fixes

Change-Id: I2e93fa3e08e6b82b26641cc736eeb1c61b04a2c0