Bug 28536: Move translatable strings into overdrive.js

Bug 28536: Move translatable strings into overdrive.js

This patch takes strings defined as variables in opac-bottom.inc for use
in overdrive.js and moves them to overdrive.js, wrapped in the
double-underscore translation function.

To test you must have valid credentials entered in system preferences
for the OverDrive API. Ideally you should test using a patron who has
holds and current checkouts in OverDrive.

Apply the patch and log in to the OPAC.

- On the "Your summary" page, open the "OverDrive Account" tab.
  - Log in to your OverDrive account.
  - The contents of the tab should display correctly, with correct
    labels for controls like "Log out of your OverDrive account", "Check
    in", "On hold", etc.
- Perform a catalog search which will return results also found in your
  OverDrive collection.
  - Open the OverDrive results page.
  - The page should display correctly, with correct labels on controls
    like "Check out" and "Place hold."

To test that the correct strings are translatable. In this example I'm
testing fr-FR:

 - Update a translation:

  > gulp po:update
  > cd misc/translator
  > perl translate update fr-FR

- Open the corresponding .po file for the strings pulled from
  JavaScript  e.g.  misc/translator/po/fr-FR-messages-js.po
- Locate strings pulled from bootstrap/js/overdrive.js for
  translation, e.g.:

  koha-tmpl/opac-tmpl/bootstrap/js/overdrive.js:124
  msgid "OverDrive account page"
  msgstr ""

- Edit the "msgstr" string however you want (it's just for testing)
- Install the updated translation:

  > perl translate install fr-FR

In the OPAC, switch to the language you're testing. Confirm that your
translated strings appear. In the above example, the string should
appear at the top of the "Overdrive Account" tab.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>