Bug 20931: JS error "ReferenceError: $ is not defined" when CircSidebar is turned on

Bug 20931: JS error "ReferenceError: $ is not defined" when CircSidebar is turned on

This patch reorganizes the way sidebar menus get highlighted based on
the current page. A global function is added to handle most cases.
Individual menu-handling scripts have been modified to handle only the
edge cases which aren't covered by the global one.

A new class is added to the global CSS file so that highlighted menu
links can be custom-styled.

To test, apply the patch and clear your cache if necessary.

View various pages to confirm that current-page-highlighting in the
sidebar menu is working correctly and that there are no JS errors in the
browser console. For example:

 - Administration -> Currencies and exchange rates.
 - Acquisitions -> Invoices
 - Tools -> Patron lists
 - Tools -> Export

And with CircSidebar turned on test various circulation pages, e.g.

 - Circulation -> Set library

Signed-off-by: Charles Farmer <charles.farmer@inLibro.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>