Bug 19500: Make module names on letters overview page translatable

Bug 19500: Make module names on letters overview page translatable

While the module pull down on adding and editing a letter is
written out and fully translatable, the overview page showed
the internal 'module code'.

Patch also renames the "Members" module into the "Patrons" module
to match Koha's terminology.

To test:
- Before applying the patch:
  - Add or edit a notice, look at the pull down for module
  - Go back to the overview page
  - Verify the module names don't match
- Apply the patch:
  - Check again, pull downs should now match
  - Verify that Members is now Patrons everywhere

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>