Bug 14199: Unify marc orgcode plugins, not overwriting existing values

Bug 14199: Unify marc orgcode plugins, not overwriting existing values

This patch copies code from marc21_field_003.pl to create marc21_orgcode.pl
for more generic use. Other fields like 040c or 040d should use it too.
Note: The plugin is used for authorities too (003, 040a).

One behaviour change is added: If the corresponding field is already
filled, it will not be overwritten.

In the unit test marc21_orgcode already replaces marc21_field_003.

Test plan:
[1] Attach plugin marc21_orgcode to a field (e.g. 003) and test it in
    the MARC editor of Cataloguing or Authorities.
[2] Check if a value is not overwritten any more.
[3] Run unit test t/db_dependent/FrameworkPlugin.t; don't be distracted by
    the noisy warnings of marc21_field_007.pl. They will be addressed on
    another report.

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>