Persistent reminders through API

[fisher60]

Once fisher60/Friendo_Site_Django#64 is implemented, we will need reminders (from the current reminder command) to be persistent between bot restarts. It should be possible to utilize all current reminder functionality and just add some additional functionality to send reminder updates to the GraphQL API and also update the local cached reminders to match the reminders in the API.

To do this, we will need to store each reminder on the database through the GraphQL API and also allow editing/deleting of reminders through the same API.

All changes to reminders will need to go to the API. It may be useful to implement a local cache of all reminders. Reminders may be changed outside of this bot, so it will be necessary to retrieve reminders from the API periodically to check for updates (keep in mind performance and scalability for querying large amounts of reminders frequently).