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)
* FIX: Emit web hooks for flags
* FEATURE: Remove 'flag' web hook in favor of 'reviewable' web hook
* FEATURE: Remove 'queued post' web hook in favor of 'reviewable' web hook
* FIX: Do not set a default value for web hooks with no events