Add ignore/unignore reports functionality for moderators.

When a thing has ignore_reports, the thing is no longer added to the moderator
cached queries (reported queue, mod queue, etc) when a user reports it.
Adjust how and when builder shows reports and big_modbuttons.

Always show big_modbuttons on spamlistings (report listing, mod listing, etc).

Only display reports if ignore_reports is False or the user is admin.
Make ignore reports button a 2-state toggle button.