qtutils: use the proper clicked signal instead of pressed

[jeff-dagenais]

Reacting to the pushed event makes the interface behave unlike any other
GUI out there. Restore the normal clicked behaviour. Fix #604 using a
bounce function.

This reverts d9a3f3f while still
fixing #604

[davvid]

There's actually a very good reason why we use clicked, not that we can't use pressed, but what this MR does is insufficient. The use of pressed was a pragmatic choice. It was the simplest because its signature has not changed between Qt 4 and 5.

This MR breaks multi-version Qt compat where the clicked(pressed=bool) callback does not always provides the pressed bool argument to the function.

In older Qt4, the argument was not provided unless you explicitly .clicked[bool].connect(...) to the signal, and the bareword one gives you a callback that doesn't include the bool argument.

In Qt5, the bool argument is provided when using the bareword signal, so the code needs to accommodate both signatures.

The full solution is to change this is to add a def wrapper(*args, **kwargs) wrapper inside connect_button() that consumes the arguments, calls the fn(), and then attaches that wrapper to the signal instead of the user-provided function.

Then you don't need the "takes care of argument mismatch" stuff, and it makes sure that we're not breaking dozens of other callsites that may or may not be prepared to deal with a change in signature.

[jeff-dagenais]

Sorry for the naive patch.

1. I am no python champion yet,
2. Although I have been using cola for 6-7 years, I have very little knowledge in the source code.

What I do know is that using GUI apps which react immediately on button pressed event hurts the brain. Feels like my mouse is broken... or is it my brain...

I definitely think we should not sacrifice the quality of user experience for a simple API signature change.

So with the provided suggestion about the def wrapper... I can give it a whirl and re-submit.

[davvid]

Sweet, thanks for the careful attention to these usability issues, I believe these changes will be well received all around, and wholly agree that user experience is more important than code simplicity.

In case it helps, here's roughly what I was describing (I guess this is where I should have added a comment about the previous choice)

def connect_button(self, button, fn):
    def wrapper(*args, **kwargs):
        """Consume clicked's callback arguments to handle differences in behavior between Qt 4 and 5"""
        fn()
    button.clicked.connect(wrapper)

Looking forward to it, and thanks again!