Status: Colorize volume icons

Use full color icons for volume. These icons match
the rest of the color theme better and are easier
to see in both light and dark themes.

Remove same-named monochromatic icons from the `panel` folder.
Symbolic icons (which automatically recolorize) are now common
so these monochromatic icons should no longer be needed.
In places where developers have chosen not to use symbolic icons,
we shouldn't force the look. This also solves an issue where
the monochromatic icons were difficult to see with mixed
light and dark themes (especially with per-app
light and dark theme preferences becoming more common).

Symlink `-panel` suffixed icons to the new
colorized icons at 16px, 22px. These still
may be used for ayatana indicators. Not sure
if any sizes other than 22px really needed.

Fixes shimmerproject#416
Address part of shimmerproject#362