Bug 16759: Make OPAC holdings table configurable

Bug 16759: Make OPAC holdings table configurable

This patch makes the holdings table in the OPAC biblio detail page
configurable using the Columns configuration tools.

This patch:
- Moves the holdingst table from plain DataTable to KohaTable
- Creates a sample yml colvis configuration for this table
  containing all the currently available columns

To test:
- Visit some record's detail page in the OPAC
- Apply this patch
- Reload
=> SUCCESS: The page shows the same information
- On the staff interface, go to:
  Home > Administration > Columns settings
=> SUCCESS: There's a new OPAC section containing the configuration for
   holdingst.
- Choose to hide some fields (both currently displayed and currently hidden).
- Reload the OPAC detail page
=> SUCCESS:
   - Required fields are hidden
   - It doesn't explode because of trying to hide stuff that is not there to start with
- Sign off :-D

Sponsored-by: DOVER
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Followed test plan, patch worked as described. Also passed QA test tool

Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>