fire wikipage.content hook on new posts

When a new post is made, fire wikipage.content hook on the inserted DOM
to trigger page content handlers such as sortable table.

Bug: 57157
Change-Id: I91076225f46c279e15dc774e3991b637a9057a2e
Flow mention should respect Echo mention preference

Bug: 60817
Change-Id: I04064a31d8d1ae2532bf6ce2ea51ca13f8777331
Associative array should not be accessed by numeric index

Change-Id: Ibe1997dde5b6488e75e17e9a90d00cc734f7c778
Merge "Flow mention should respect Echo mention preference"
Merge "Associative array should not be accessed by numeric index"
Merge "fire wikipage.content hook on new posts"