Replace unmaintained dep `react-native-orientation`.

[chrisbobbe]

When we upgrade to RN v0.60.0 (that's #3548), we'll get this warning:

warn The following packages use deprecated "rnpm" config that will stop working from next release:
  - react-native-orientation: https://github.com/yamill/react-native-orientation#readme
  - rn-fetch-blob: https://npmjs.com/package/rn-fetch-blob
Please notify their maintainers about it. You can find more details at https://github.com/react-native-community/cli/blob/master/docs/configuration.md#migration-guide.

rn-fetch-blob is easy to fix; we just have to upgrade to v0.11; I'm planning to do that in my PR for #3548.

react-native-orientation is unmaintained, though. The fix for this warning is very simple, but the PR for it has gathered dust, and the repo isn't getting updates.

This will take some assembly in native code, which should all be spelled out in the replacement library's installation instructions.

I recommend trying Expo's ScreenOrientation; Expo libraries are generally frequently maintained, and we can newly use them since #4016 landed. If we're going with that, we'll follow the instructions for a "bare React Native app" (ours isn't "managed" by Expo), and use yarn add expo-screen-orientation instead of npm install. Since Expo uses TypeScript instead of Flow, we'll have to put together a libdef, unless FlowTyped has one (I don't think it does). We have a new doc for that, and it would be nice for that to be updated with anything new we learn along the way.

[chrisbobbe]

Huh, it would seem that we may actually want DeviceMotion, not ScreenOrientation...

From the ScreenOrientation doc:

Screen Orientation is defined as the orientation in which graphics are painted on the device. For example, the figure below has a device in a vertical and horizontal physical orientation, but a portrait screen orientation. For physical device orientation, see the orientation section of Device Motion.

[chrisbobbe]

Huh, it would seem that we may actually want DeviceMotion, not ScreenOrientation...

Ah, no, actually (at least on iOS; haven't tested on Android yet) — when I followed some alternate suggestions for the AppDelegate.m, defaulting to a lock of ALL orientations allowed, it does indeed respond to physical device rotation

And, it works on Android too!

[gnprice]

Cool. I suspect what that means is: "orientation" means how the display is oriented on the device -- which is often controlled by how the device is oriented physically, but may not be (e.g. with "orientation lock" mode.)

So if you really are interested in how the device is oriented physically relative to gravity, you want the other thing -- but we're interested in how the display is oriented on the device.

[chrisbobbe]

but may not be (e.g. with "orientation lock" mode.)

Yeah. What isn't clear in their setup instructions for what to put in AppDelegate.m is that the "default orientation" really seems to mean an orientation you'd like to lock to, and have difficulty changing to a different lock later. So I locked to allowing "all" orientations.

The line in the instructions that threw me off, I think, is this, from here:

or if you want to change the default screen orientation, with:

[chrisbobbe]

Hmm, that's not quite it. That tweak seems to affect the supported device orientations, which makes sense—not "orientations you'd like to lock to and have difficulty changing later". See the Apple doc. (Incidentally, it would be quite easy to support all orientations except upside-down, if we think it's a bit silly to allow the upside-down orientation.)