Bug 26734: (follow-up) Replace db update with backup and default

Bug 26734: (follow-up) Replace db update with backup and default

The inline update of variable for the notice template was proving
troublesome.. this patch replaces it was a backup of the existing notice
followed by replacing the notice with the default.

Test plan
1/ Run the database update
2/ Check that the templates have been replaced by the defaults (for all
languages enabled)
3/ Check that a backup of the original notices was made by naviagating
to view the action log (/tools/viewlog.pl) and selecting 'all modules' +
'all actions'

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>