Bug 15287: Use font-awesome on the OPAC

Bug 15287: Use font-awesome on the OPAC

This patch replaces Bootstrap's glyphicons with Font Awesome icons.

To test, apply the patch and clear your browser cache and regenerate the
OPAC CSS from the LESS file if necessary. Check these icons and confirm
they look correct:

- Cart and Lists icons in the OPAC header
- User icon in the header when the browser window is narrow
- Languages menu when multiple languages are installed and
  the OpacLangSelectorMode system preference is "top" or "both top and
  footer."
- Set the  SuspendHoldsOpac system preference to "allow" and log in to
  the OPAC as a user who has one or more holds.
  - Check the appearance of the "suspend" and "resume" buttons both in
    the table of holds and at the bottom.
- With one or more clubs defined, log in to the OPAC and check the
  "Clubs" tab on the user summary page. The "Enroll" and "Cancel
  enrollment" buttons should look correct.
- On the "your messaging" tab in the OPAC, the "Digests only"
  information icon should look correct.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>