Add support for multifields in custom column

You can now add column with Custom type with more than one field
by using OR "||" splitter.

Bug: 9695

Change-Id: Ia82a91e7a35b867647d36cb9626e3870f46c0d85
Reviewed-on: https://code.wireshark.org/review/5804
Petri-Dish: Michal Labedzki <michal.labedzki@tieto.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Michal Labedzki <michal.labedzki@tieto.com>