Skip the "Result" page for most tasks (eliminate extra page load)

Many of the "task" work flows present a status message + "Done" button on a separate page (Result.php) after the processing is completed. We can streamline these by removing the extra page load and returning to the URL that the task was launched from with a "session" status msg displayed on top of the page.

NOTE: Delete Contacts (from search tasks) already works this way. I think most of this is handled in the Controller - so might make sense to do this "globally" for all tasks that use Result.php. Otherwise, let's do it for the following specific tasks:

Add Contacts to Group from contact/search
Add Contacts to Group from group/search?context=amtg : For this situation we should return to the amtg page (Find Contacts to Add to $title Group) with the previous search preserved.
Add Contacts to Event, Organization, Household.
Record Activity for Contacts
Remove Contacts from Group
Tag Contacts
Untag Contacts

— original discussion at —
http://forum.civicrm.org/index.php/topic,14776.msg63033.html#msg63033