Bug 27491: Rename system preference opaclanguages to OPACLanguages

Bug 27491: Rename system preference opaclanguages to OPACLanguages

Test Plan:

1. Go to Administration
2. Go to System Preferences
3. Find 'opaclanguages' (note the lack of capitalisation)
4. Apply patch
5. Repeat step 1 and 2
6. Find 'OPACLanguages' (note the use of capitalisation)

Signed-off-by: Barbara Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>