quick settings 3: Network cleanups

Before getting serious about moving the network indicator to quick settings, apply a couple of cleanups.

There aren't any UI changes yet, other than a massive simplification of status labels.

The most involved commit splits out the ad-hoc network tracking from the wifi-selection dialog into a new WirelessNetwork class. Incidentally, that also neatly isolates the one bit of the dialog that is worth preserving 😉