Redundancy in alsabar and pulsebar widgets

[lcpz]

It would be better to have a single widget, named bar, which can be feed with volume data from either ALSA or PulseAudio.

[gregflynn]

Before knocking this out and sending you a PR, what do you think of this approach:

• create a new widget volumebar to encompass common functionality and have an argument to switch between alsa and pulse
• modify alsabar and pulsebar to wrap the volumebar widget to preserve backwards compatibility
• somehow deprecate alsabar/pulsebar in the wiki or logging a deprecation warning

:+1: :-1: ?

[lcpz]

Sounds good.