Add pressed state for windows buttons

[grulja]

Fixes #60

[grulja]

@TheBoctor can you please test? :)

[TheBoctor]

The colors all appear consistent with the screenshots in #60, and the pressed state mostly works as expected.

However, if the user clicks and drags outside of a button to trigger maximization, as described in #58, any further left clicks inside the Qt app window will cause the last pressed button to assume the pressed color. This persists until one of the buttons is clicked and released, without the cursor leaving its area.

[grulja]

However, if the user clicks and drags outside of a button to trigger maximization, as described in #58, any further left clicks inside the Qt app window will cause the last pressed button to assume the pressed color. This persists until one of the buttons is clicked and released, without the cursor leaving its area.

What about now?

[TheBoctor]

Looks good now. The pressed color changes back to normal as expected, as soon as the user interacts with the window.

[grulja]

Looks good now. The pressed color changes back to normal as expected, as soon as the user interacts with the window.

Thanks for testing. I tested it myself before, it's not like I'm blindly pushing changes, but I wanted someone to double-check and I'm glad I did that, because you spotted an issue.

[TheBoctor]

Looks good now. The pressed color changes back to normal as expected, as soon as the user interacts with the window.

Thanks for testing. I tested it myself before, it's not like I'm blindly pushing changes, but I wanted someone to double-check and I'm glad I did that, because you spotted an issue.

No worries. I assumed you were also checking everything, but an extra set of eyes never hurts. Thanks for fixing this.