Send create message when undeleting posts

[simen]

Subsystems like reaktorcore that count the number of posts in certain categories uses delete actions in grove to decrement these counters. If someone were to undelete these posts, they will magically reappear without triggering a positive count. Also they may not be reindexed in the search index of sherlock.

Posts that are undeleted should be announced on the river as if they were just created.

[This is a minor concern since no-one is actually using the undelete facility yet.]