Better methods for saved messages.

Most subclasses should only need to customize the message text in getSavedMessageText() but add a few methods to allow subclasses that need more control of the whole process.
One line is simplier than two.
Add convenience methods for all the saved message properties.

It's still faster to overide the getSavedMessage() method if you want to do more than a couple of things, but these should help common cases.
Rename getSavedMessageText() to getSavedMessagePrimaryContent() to be more consistent with other message methods.
Merge pull request #16 from isaacgrant/admin-object-edit-improvements

Better methods for saved messages.