Images resource should allow sorting

Currently the images resource orders the result set on the time the images were added to Imbo, in a descending fashion.

This should be made configurable via an query parameters:

Examples:

* `?order=size:desc`
* `?orderBy=size&order=desc`

Preferences?

The resource should also be able to filter images on for instance extension/width/height/mime-type and so forth.