Resetting Region keeps original el

Factored out this part from my original PR #1705 to re-address #1673.  Pretty straightforward, but definitely needs eyes on it considering what happened from my last PR :disappointed:
and only now do I realize that region is not a real Marionette object :(
at somepoint this guys should really extend from Marionette.Object

but this is not related to this PR, just a note :paperclip: