Added imageQuality option, which is passed to the canvas.toBlob method to save resized images.

Removed mozGetAsFile code from the image processing plugin, as Firefox
supports setting the FormData filename since version 22 (current
version being 25).
Added imageForceResize option, to force writing to and saving images from canvas.

This will also process images via canvas that fit the maximum
constraints.
Added imageType option to force the type for the image saved from canvas.
Added imageQuality, imageType and imageForceResize options.