Publish UI Demo to Expo

[lukecyca]

Publish our app to http://expo.io as an unlisted (I think?) app. Get the resulting QR code and put it in the README.md of this repo.

Instructions for the public to try out our demo:

• Download Expo from the app store
• Open it and scan this QR code

[lukecyca]

I've published this app to: https://expo.io/@mycoralhealth/mycoral-patient

Currently it's unlisted, so anyone with the link can see it but it's not in Expo's directory.

[lukecyca]

Setting this up has been a struggle because it doesn't seem to be possible to create a "Team" or "Organization" account on Expo.io, so that we can all publish to the same app URL. Worse, my expo account was linked to my github account, so to share access I would have to share my github credentials!

My solution is as follows:

• I have created a new account mycoralhealthdev with a username/password we can share. This is where we'll publish development apps, and we can use this account when developing locally (so that WebAuthentication and other Expo features work).
• I have modified the original account mycoralhealth to just use a username/password, and unlinked it from github. I will hold this password (or share with Andy/Nick) and we will use this only for publishing public releases.

[lukecyca]

To clarify the new workflow, you must use the exp tool, and be logged in for the app to be able to use Expo features:

mbp:mycoral-patient luke$ exp login
? Username/Email Address: mycoralhealthdev
? Password: ************

Success. You are now logged in as mycoralhealthdev.
mbp:mycoral-patient luke$ exp start
...
[QR Code]
[exp] Your URL is: exp://a5-fdh.mycoralhealthdev.mycoral-patient.exp.direct:80

Use the QR code on your phone, or copy that URL into the iPhone simulator.