Add network connection endpoint

Add ability to set `airplane_mode`, `wifi`, and `data` in Android. 

At the moment there are problems with keeping `adb` alive. Twiddling the network settings tends to kill the adb connection, so the calls are wrapped in calls to `wrapActionAndHandleADBDisconnect`. However, periodically there is a problem where `adb shell echo 'ready'` fails with 

```shell
error: Error running shell echo: Error: Command failed: error: protocol fault (no status)
```

This might be a case where retrying might work. But my brain is fried. I wanted to put this out there to see if there were any ideas.

Depends on https://github.com/appium/appium-adb/pull/20
Ah. That didn't get in. Yes, works for Selendroid.