fix and enable reminder notifications

[erosson]

See #6 - we removed the reminders setting for our first release, as it was broken. Re-enable it and fix it.

[erosson]

https://docs.expo.io/versions/latest/sdk/notifications/#localnotification

OneSignal was used for push notifications. I'm not sure I have a use for push here - if we drop push notifications and settle for recurring local notifications, things get much simpler.

[erosson]

implemented local push notifications. I've forgotten what text quirk used here, and it's not in the source code - so I'm leaving this disabled for a few days before releasing, so I can see some of quirk's notifications and compare my wording.

usually I prefer feature-flagging to branching, but I'm not sure how best to do feature-flagging on mobile - #14 - so for now, this is in a branch

[erosson]

if we drop push notifications and settle for recurring local notifications,

Unfortunately, there was a good reason for push notifications:

Important Android limitation: Local notifications are cleared when an Android device is restarted.

Showstopper for this feature on Android. (Could release it ios-only, though...)

Fortunately, there's a feature request with a recent PR on that page; expo-notifications seems to fix this: https://www.npmjs.com/package/expo-notifications

Not yet usable with ejecting, but it sounds like that will change soon. Expo 38 is supposed to be end of June, I'm in no hurry, and am waiting to see more of quirk's reminder text anyway - so let's wait this one out.

[erosson]

Showstopper for this feature on Android. (Could release it ios-only, though...)

Sure, why not - released on ios in 1385632