Bug 10320 - Integrate OverDrive search into OPAC (1/2)

This show results from the OverDrive ebook/audiobook service in the
OPAC.

To test:

1) Fill in the OverDrive system preferences (you will need an Overdrive
client key, client secret and library ID).
2) Perform a search on the OPAC, verify that, if available, a link to
results from OverDrive will appear at the top.
3) Click on the link, verify that the list of results appears.
Bug 10320 - Integrate OverDrive search into OPAC (2/2)

This followup adds the sysprefs and copies the relevant JS to CCSR.
Bug 10486 - Allow external Z39.50 targets to be searched from the OPAC (1/2)

This adds a new page to the OPAC that can search several Z39.50 targets
using Pazpar2.

Test plan:
1) Apply patches.
2) Update database.
3) Add one or more Z39.50 targets, using the Administration -> External
   targets screen. Note that not all targets support keyword search, but
   here are some that do:
     * Library of Congress: lx2.loc.gov, 210, LCDB, none, none, MARC21, UTF-8
     * BNF2: z3950.bnf.fr, 2211, TOUT, Z3950, Z3950_BNF, UNIMARC, UTF-8
4) Perform a search on the OPAC, check to see if the "external targets"
   notice pops up at the top.
5) Click on the results link near that message.
6) This should bring back results from all enabled targets, all of which
   should be clickable to bring up a detailed view of the record.
Bug 10486 - Allow external Z39.50 targets to be searched from the OPAC (2/2)

This adds a syspref to allow toggling this behavior.