Support for shrinking images

Added an option to Inline Image Viewer (showImages.js) to allow for shrinking of imgur images.

A modification of this previous pull request: https://github.com/honestbleeps/Reddit-Enhancement-Suite/pull/1506
it would be more efficient to reuse a regexp here rather than define a new one every time. we're talking micro optimization on a tiny level here, but still it would be best to update :-)