Having three widgets for volume led to a problem of code duplication -
same logic was duplicated three times. However when an issue was
discovered and fixed, it was fixed in only one of three widgets.
So I decided to create a volume widget from scratch, adding new
features, such as selecting input/output, better responsiveness,
easily customizable widget ui (bar, text, icon, icon and text, arc).
Should close#199, #198, #185, #182, #47, #122, #183.
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