Migrate Majel to Slash Commands

[kkotenko]

Discord recently introduced the ability to use Slash Commands. While it seems they require a bit more setup upfront, they

• are more user-friendly (user can see all the command options on typing)
• new commands seem to be somewhat nicer to implement

To be evaluated:

• How hard is the setup, really?
• How do Slash Commands behave if multiple bots try to register the same Slash Command (eg /version or /2d20)?
• Would switching to Slash Commands require changing syntax (e.g. /2d20 becomes /roll 2 20 because it's not clear to me if it is possible to include (semantically) parameters as part of the command)

[engooyen]

In the works.