Adds "All Data" filter to case list report

Addresses this ticket:
http://manage.dimagi.com/default.asp?121778#688842
It adds an "All Data" filter by modifying the `CaseListMixin` class that is subclassed by `CaseListReport`. I've examined the code of `CaseListReport`'s descendants, and none of them seem to cause conflicts with the changes made.
Outer parens not needed.

Could also eliminate the try/except with `getattr(self, "show_all_filter", False) or ...`. I think that would be equivalent since `self.show_all_filter` is always true if present, but maybe I got that wrong in which case the meaning would be changed slightly by using `getattr`.