Remind command

[RaasAhsan]

Schedule a reminder with a description for Naomi to highlight you (or somebody else) at some later time. should probably persist these to sqlite

Possible usage

!remind 2 days - @nate give me plex
!remind "2 days 3 minutes" @nate give me plex

!remind "8/1/2018 12:00:00pm" it is august 1st!

We can use https://momentjs.com to parse absolute/relative times

Questions to address:

1. What command format will we want to use?
2. How should we handle timezones? Should the bot use a fixed timezone, let the user specify timezone as part of the string, or should we even store a per user configurable timezone?
3. What time granularity should we search for and push reminders? 1-minute seems good