Bug 18403: Send logged_in_user to template from C4::Auth

Bug 18403: Send logged_in_user to template from C4::Auth

Technical note:
To ease future changes we are passing a logged_in_user variable to templates.
It contains the Koha::Patron object representing the logged in patron.
This will be very useful for this patch and even after (for instance we will be
able to replace easily loggedinusername and loggedinusernumber).

Signed-off-by: Signed-off-by: Jon McGowan <jon.mcgowan@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>