WIP: Migrate to expo

[youngkidwarrior]

This is an exploratory PR about migrating the BrightID app to expo. I basically patched it together to get it compiling and haven't taken any steps to fix anything. Some things are broken.

The main reasonings for moving to expo are as follows:

• Much simpler to upgrade to new versions of react native (expo upgrade)
• Easier interop with app stores. EAS Build, EAS Push, EAS Submit. Should save us a lot of time
• More easily shareable testing environment for dev branch with Expo Go
• Better DX experience with Expo Go and no native compile step (removes gradle and Podfile)
• Proper CI/CD using EAS build

Switching to expo should help BrightID spend less time with react native bugginess and App store updates and more time building the app. It's a massive pain to switch, so I understand pushback, but it would be a massive boost to long run productivity and app health

Here is a checklist of definitely broken things (there may be more):

• keychainAdapter
• ChangePasswordModal
• fsStorageAdapter
• No support for fetch-blob
• Push Notifications
• Localization
• React Navigation TS Errors
• Tests: Haven't dared to run these yet
• Possible: DisplayName was deprecated. Switch to firstName + lastName.