Bug 14957: (QA follow-up) Rename 'merge' => 'overlay'

Bug 14957: (QA follow-up) Rename 'merge' => 'overlay'

This patch acknowledges the fact that 'merging' has a different meaning
in Koha than the behavior this great patchset introduces. The more
idiomatic way of describing the behavior is to talk about 'overlay rules'.

This patch also:
- Fixes kohastructure.sql missing table encoding a collation
- Fixes the atomic update completely missing a table
- Moves the syspref entry to 'Importing', probably a rebase issue

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Bug 14957: (QA follow-up) Fix syntax error in atomicupdate

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Bug 14957: Fix imports in tests

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Bug 14957: Fix imports in marc-overlay-rules.pl

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Bug 14957: Fix syspref's values

It didn't switch off when set to "don't use"

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
JD amended patch: Fix license statement

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>