[HPT-124] When page editing is called from paged view, return to paged view upon submission.

This introduces a session key "came_from" whose value names the object
type (:paged, :page) which requested the edit.
Return to the owning paged (if there is one), not the list of pageds.
[DS-124] Wrong helper was generating wrong return URLs.
Merge pull request #20 from mwoodiupui/HPT-124

[HPT-124] When page editing is called from paged view, return to paged v...