utils: slugify text function addition

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
search: collection template loading

* Introduces collection specific templates "collection_{name}.html" with
  fallback to the default "collection.html".

Reported-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
Signed-off-by: Charalampos Tzovanakis <drjova@cern.ch>