Post return vals

Does the very best to handle API returns in a meaningful way:

When called as an API, post results will:

* Default forward() to / is disabled
* If postContent() returns nothing (null) then we
 * Set a 400 response
 * Set an error message if no messages have been set
* If postContent() returns something then
 * if it's ===false we set 400
 * We return the result in the current template

(Closes #586 )