Add a volume bar

[deep-gaurav]

From https://github.com/deep-gaurav/rusty_pipe/issues/7

I think it can benefit from a volume bar. As of now, the only way to lower the volume on a computer is to install an extension like 600% Sound Volume to control the volume for each tab. The other way, of course, is to lower the device volume, but that'd also decrease the volume of everything else.