dmarc_view_reports: negating search conditions

[richlv]

It would be useful to negate some search conditions.
For example, when results of a certain author or domain have been reviewed, it could be useful to exclude them.

Parameters that could benefit from this:

• author
• from_dom
• disposition

Parameters that have only two options like SPF/DKIM could support this for consistency, but the functional gain seems to be minimal.