* Add "Reference" section to Issue view sidebar
* Removed unneeded tailored CSS, added Fomantic UI classes
* Removed tailored CSS in favour of HTML-only approach
Kindly provided by @Gusted
* Added i18 translation key for reference link string
* Corrected spelling of "References:" to "Reference:" for reference link text
* Removed `Issue.ReferenceLink` in favour of a local template variable