Here are two new prompt pop-ups: ok_cancel and yes_no_cancel. (#1)
Here are two new prompt pop-ups: ok_cancel and yes_no_cancel. (#1)

* Added two new prompt pop-ups: ok_cancel and yes_no_cancel.

ok_cancel allows the user to select either ok or cancel, and behaves like prompt.question.
yes_no_cancel allows three options: yes -> True, no -> False and cancel -> None.

* Added default button to ok_cancel, yes_no, and yes_no_cancel in prompt.

Note that question has been renamed to yes_no.

* Cancel now always returns None

Plus other edits to make it more pythonic and consistent with rest of code

MSLNZ/msl-qt