CRM-15578 - crmMailing(AB) - Submission & status tracking

When loading or submitting, determine the status of any jobs tied to this mailing.

When attempting to edit a submitted mailing, display a message instead of a form.

Change the technique for updating URL -- instead of watching 'mailing.id',
explicitly call updateUrl after saving.  This ensures a consistent, linear
sequence of operations.  (Note: The watch technique was useful when there
were different variations of save() in EditMailingCtrl and
PreviewMailingCtrl, but we eliminated PreviewMailingCtrl, so it's much
easier to manage the dataflows in a centralized fashion.)
Remove unused imports
edit-split.html - Remove unused file
CRM-15578 - crmMailing(AB) - Refine pageflow:

 * "Submit" => leave()
 * "Delete" => leave()
 * "Save" => updateUrl()
 * "Send Test" => updateUrl()

This commit also switches back to managing pageflow from the controller
(rather than calling .then(leave) in the .html).  At the moment, it seems
more useful to have all the different composition screens follow the same
pageflow (rather than allowing them to have different pageflows).