The restore feature was not working properly. When pushed, the button
was removing the notification from the admins panel, but it was not
restoring in the proposal.
I added an `after_restore` function (that I missed in the first PR)
so that the notification is unmarked as moderated.
Add new routes for the proposal notifications edition and
abilities to let moderators edit it (mark as ignored, hide, etc.).
The notifications are not flaggable because they doesn't work like that,
but in a similar way. The moderator/administrator is in charge of hidding
them through the UI, so the normal users don't flag it as inappropriate.
New controller Moderation::ProposalNotification to manage the moderators
work.
