Prompt Popups working on KDE Plasma (and maybe other DEs)

[dabberoo]

This is a fix for #162 on KDE Plasma, but I think a similar approach could be used for other desktop environments with the same issue. This also preserves the changes made in 1d88034

Thanks to TotallyNotAnAccount's feedback on the original thread I abandoned trying to get the prompts to work with overrideredirect(True). The approach I settled on creates Prompt Popups with the following:

• a bordered window with its own icon in the task bar (tradeoff)
• min, max and close buttons removed from the window border
• window cannot be closed through the task bar
• non-resizeable
• renders below Popups but above all other windows (tradeoff)
• can be moved around with the mouse (tradeoff, couldn't find a simple way to disable this)
• can now take focus and receive text input

Tested on Wayland