Spam reporting patch (#9)

Spam reporting is available for trusted users (org members and admins) via a
button on a spammer's profile page;
a new section Site Administration > Identity & Access > Spam Reports;
a new "pending spam reports" indicator in the header for admins.

See #7 for the code review.

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Co-authored-by: Oleg Komarov <[email protected]>

Author: komarov