base: footer modified

* 'submit' text and link swapped out for 'deposit'

Signed-off-by: Jake Cowton <jake.calum.cowton@cern.ch>
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>