Bug 1001724: don't display EXIF preview images if aspect ratio does not match

media frame changes to use #-moz-samplesize if the exif preview is no good

set a maximum size for MediaFrame so photos are downsampled even when previewed in the camera

specify a maximum image size for all MediaFrame objects so large JPEGs can be previewed

use cropResizeRotate in the gallery metadata parser to improve thumbnail generation efficiency

fix failing test, add new media frame tests, remove logging statements

Modify camera filmstrip code to not use distorted exif previews for thumbnail creation

Handle downsampling with the downsample.js utility to get scaling right
Merge pull request #18811 from davidflanagan/bug1001724-v1.3t

Bug 1001724: don't use distorted EXIF previews, generate thumbnails more efficiently, enable previews of large jpegs r=russnicoletti