Slash Command - xkcd search emphemeral

[Plyb]

depends on #16

xkcd search should confirm with the user using ephemeral messages that it has found the comic they wanted, allowing the user to cancel if it has found the wrong one.

[AverageHelper]

Since this would involve multiple interactions of different types (slash command + button) and potentially concurrent invocations by multiple users, we would need to keep track of the interaction in the database. Shouldn't be difficult, but would take some planning

[gmacgre]

I'll take this chance here to add on the additional feature of search by term instead of by number. For now, it only searches by order number but this would be a good chance to add in searching by a related term.