Bug 20966: (follow-up) Add template variable filter; Fix table export

Bug 20966: (follow-up) Add template variable filter; Fix table export

This patch makes to corrections:

1. The "$raw" filter has been added to the column configuration
2. The columns configuration now specifies which columns are exported in
   Copy, Excel, etc. operations.

To test, apply the patch and test the various table export buttons on a
both a closed and open basket. Confirm that the 'Modify' and 'Cancel'
columns are not exported.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
https://bugs.koha-community.org/show_bug.cgi?id=20996

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>