Add support for bulk-updating multi-line translations

http://manage.dimagi.com/default.asp?146611

@amsagoff this seems like a new feature since the old parser definitely did not support multi-line translations with un-escaped newline characters. Does this seem like a win to you?
In Python3 you can use [`nonlocal`](https://docs.python.org/3/reference/simple_stmts.html#nonlocal) to do this type of thing.