When a user marks that another photo should have been marked as explicit:
* The owner of that photo gets a notification about it, which reminds them of
the explicit photo policy.
* The photo's "Flagged" boolean is set (along with the Explicit boolean)
* The 'Edit' page on a Flagged photo shows a red banner above the Explicit
option, explaining that it was flagged. The checkbox text is crossed-out,
with a "no" cursor and title text over - but can still be unchecked.
If the user removes the Explicit flag on a flagged photo and saves it:
* An admin report is generated to notify to take a look too.
* The Explicit flag is cleared as normal
* The Flagged boolean is also cleared on this photo: if they set it back to
Explicit again themselves, the red banner won't appear and it won't notify
again - unless a community member flagged it again!
Also makes some improvements to the admin page:
* On photo reports: show a blurred-out (clickable to reveal) photo on feedback
items about photos.
