WebSearch: custom i18n collection boxes

* Enables per collection customization (and internationalization)
  of collection boxes labels "Focus on", "Narrow by" and
  "Latest additions".  (closes #1286)

* Updates demo data to showcase custom names in 'Videos' and
  'CERN Divisions' collections.

* Adds new table 'collectionboxesname', and related upgrader
  script.

* Adds regression tests and amended admin guide accordingly.

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>