Bug 16237: Allow entering of EDI accounts with plugins disabled

Bug 16237: Allow entering of EDI accounts with plugins disabled

Test plan:
  1. Disable <enable_plugins> in koha-conf.xml (restart memcached if needed).
  2. Open the EDI accounts admin page.
  3. Notice incredible breakage.
  4. Apply patch.
  5. Reload page, should now display (and the "Plugin:" dropdown should
     be hidden).
  6. Re-enable <enable_plugins> (and the UseKohaPlugins syspref as
     well).
  7. Ensure that the "Plugin:" dropdown is once again displayed.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan Gallagher <bredan@bywatersolutions.com>