QTile: Dynamically Generate Bar Widgets

[bastisawesome]

Currently to get multi-screen support (particularly with the same bars), I've got each bar being created as a custom object. It may be better to use a function to generate the bars, particularly some helper functions to generate the widget list.

For example:

...
def init_bar_widgets() -> ...:
    widget_list = [...]
    return widget_list

screens = [
    Screen(top=bar.Bar(widgets=init_bar_widgets(), ...),
    Screen(top=bar.Bar(widgets=init_bar_widgets(), ...),
]
...