Allow entering notes in Whitelist

[codeling]

As an administrator, I should be able to enter notes to a whitelist entry (e.g. username or reason why). Suggested by @nighteyes2014.
Reference: #86

The current whitelist holds a "date" entry, which serves no purpose (other than a possibility to document the creation or modification date, but that has to be done manually); this will be removed in favor of the note field.