ammendment: generic, environment-aware cleanDb task and minor build improvements
fixes in frontend controllers and corresponding backend classes
* re-introduces getRelated() to IDictionary
* corrected setter calls in ruby to get_previous entry
* added retrieving a get()-call to retrieve an actual entry instead of Optional<*>
* details page template now renders real content of entries (htmlDescriptions if possible, otherwhise description field
* removed unused DbHelper mixins
suggestion of alternative background CSS-styling that results in a more uniform background design when switchin bestween detail pages with a big difference in the length of the given test.