Bug 29757: Add filters for reversable offsets

Bug 29757: Add filters for reversable offsets

This patch adds filtering methods for (non)reversable offsets.

To test:
1. Apply this patches
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Account/Offsets.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>