Typo fix in plugins.go

(cherry picked from commit 4e160eab)

Call termination:
Current code attempted to re-use headers from the original message (Pub)
in order to form a replacement message
while calls normally terminate on Note messages which don't have headers.

Add "sender" header for messages sent on_behalf_of

Allow root to find suspended and soft-deleted topics and accounts

Fix root user handling in init-db