Bug 31379: Change results per page text for default

Bug 31379: Change results per page text for default

Since Bug 14715, one can change number of results per page.
The actual text in combobox for default value is : "Library default:
20"

This text is hard to translate correctly.
For example french translation use "site par défaut" wrongly meaning
"default library".

I propose to simply use "20 (defaut)".

Test plan :
1) Go to system preferences and set both 'numSearchResultsDropdown' and
   'OPACnumSearchResultsDropdown' to 'Show'
2) Do a catalogue search in the intranet using a search term that will
   bring lots of results
3) Look at restults per page combobox
4) Same for OPAC

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>