Add support for direct responses

[roborourke]

Sometimes in the case of slash commands it's useful to have the users command displayed too - it helps to educate / show other users how to use a command they may not have seen before.

It can also add context to a response rather than the response having to indicate what just happened when it's visible to all users.

Without a direct response

What I see:

Me: /do-thing
Bot: Thing done!

What everyone else sees:

Bot: Thing done!

With a direct response

Everyone sees:

Me: /do-thing
Bot: Thing done!

[roborourke]

@johnagan this is pretty well tested now in my current use cases, let me know if you have a better solution in mind.