Added Image Shrink module

Basically, the image shrink module lets users choose a maximum image size for imgur images if they don't want to have to load extremely large images. For instance, a 5000px wide image of a few words doesn't need to be loaded when it can be seen perfectly fine at 1024px. It uses imgur's thumbnails, specified here: https://api.imgur.com/models/image#thumbs. Whenever an image is shrunken, a link to the original image is added to the post as well.
also, for security concerns, please don't use innerHTML.  Instead, use .safeHTML() or build up the elements in JS and set attributes / textcontent.  (for reference: https://github.com/honestbleeps/Reddit-Enhancement-Suite/commit/31095d476748166a0680eba72b4c4722d222a465)