[suggestion] xfce4: replace battery monitor plugin with the power manager plugin by default

My device is an Asus TF101. It's a special convertible device that has two batteries: one from the tablet itself and one from the dock. With the current battery monitor plugin, I can only see the main tablet battery.

Besides that, it also offers the brightness control of the device more accessible.

My suggestion is to replace the battery monitor xfce plugin with the power manager one.

Before:

After:

See that I can easily control brightness now and both batteries are detected and showing.

@Jakko