[plugin] AirPlane Mode

Hey there! I've put together a little plugin to mimic airplane mode in koreader. I rarely take koreader out of the house, but when I do it's a mad button dash to remember what all needs to be disabled so koreader doesn't lock up trying to reconnect to my home network. I tried to use the profiles plugin, but the use case didn't quite fit what profiles was designed for.

What It Does

Hitting the checkbox for "AirPlane Mode" in the Network tab will disable all automatic wifi settings, as well as a list of the standard plugins that use automatic networking. I don't offer a way to add to the list the plugin monitors (yet? adds to TODO...), but the plugin does honor already disabled plugins. Happy to add more to the list while I find a clean way to manage what plugins you want to include.

Repository, tarball, and zip with the initial alpha can be found here: https://github.com/kodermike/airplanemode.koplugin

Tested with:
* the koreader emulator (of course)
* Kobo Clara
* Kobo Clara2E
* Kobo Forma
* Kobo Libra Color

I know it's a kobo heavy list, but it's what I had on hand while testing.