CE-1125 ImageReview refactoring - Prologue

This PR contains:
* Use Vignette as a thumbnailer
* Logging an action performed on every image
* The beginning of a code separation (hooks & db queries)
* Some documentation

Pinging @Grunny @macbre and @nmonterroso  due to Vignette changes
Single quotes are preferred per coding conventions unless using interpolation.