Back end image pre-generator

[Swader]

Glide currently resizes images on-demand, when they're requested and if they're allowed. Sometimes, however, a user might want to generate these images well in advance.

Build a UI which would bypass the size restrictions of the current ImageController and allow for manual input of a file and all sizes a user wants to generate from it, then generate those images into the public folder ready for use. The uploaded image would be stored into the assets/image folder as usual.