X.H.StatusBar: Add statusBarGeneric for taffybar/trayer/stalonetray
X.H.StatusBar: Add statusBarGeneric for taffybar/trayer/stalonetray

`statusBarGeneric`: A generic `StatusBarConfig` that launches a status
bar but takes a generic `X ()` logging function instead of a `PP`. This
has several uses:

 * With `xmonadPropLog` or `xmonadPropLog'` in the logging function, a
   custom non-`PP`-based logger can be used for logging into an `xmobar`.

 * With `mempty` as the logging function, it's possible to manage a status
   bar that reads information from EWMH properties like `taffybar`.

 * With `mempty` as the logging function, any other dock like `trayer` or
   `stalonetray` can be managed by this module.

Related: https://github.com/xmonad/xmonad-contrib/pull/463

xmonad/xmonad-contrib,xmonad/xmonad-contrib