Allow placeholders in battery status (change order of evaluation)

Currently there's the format text which defines a message structure common to all three statuses except for the %status value. So a simple idea to define different message structures for different statuses is just to set format = "%status" and then set three different full messages, one for each status. The problem with that approach is that %status seems to be replaced after other placeholders were replaced. So I'm suggesting to replace it the first. I think this is a simple change that address problems nowadays handled in a more ad hoc fashion (for example, hide %remaining when charge is 100%). One use case is to completely hide the battery indicator when the battery is full and the computer is plugged in.

I could open a PR if you like the idea.