Previously, if an admin user tried to add/remove
users to another user's ignored list, it would
be added to their own ignore list because the
controller used current_user. Now for admins only
a source_user_id parameter can be passed through,
which will be used to ignore the target user for
that source user.
This reverts commit 20780a1eee.
* SECURITY: re-adds accidentally reverted commit:
03d26cd6: ensure embed_url contains valid http(s) uri
* when the merge commit e62a85cf was reverted, git chose the 2660c2e2 parent to land on
instead of the 03d26cd6 parent (which contains security fixes)
