Add /greet command

[yawboakye]

Some Slack communities cuts across time zone, and that's a good thing. That also means that it's very likely the person you want to talk to is in a different time zone than yours, which means you can't start the conversation with a Good morning without confirming that they're in their morning hours.

/greet removes that headache. All you have to say is /greet @username, and you have the appropriate English greeting chosen and presented to them.

[Kessir]

Hi @yawboakye . Any update on this?

[silentworks]

We don't have https on our heroku instance, hence why this has not been attempted as yet.