Replace `AbstractCommand` with `CommandTree`

[Ernest314]

Depends on #266, and supersedes #98.

Classes to convert:

• [x] About
• [x] Cap
• [x] ClassDiscord
• [x] Help
• [x] Invite
• [x] IreneStatus
• Minigame
• MinigameScore
• [ ] Raid
• [x] Random
• [ ] Rank
• [x] Roles
• [ ] Slowmode
• [ ] Solve
• [x] Starboard
• [ ] Tag

[Ernest314]

Remember to include help fields (this can also be called by the /help command maybe?)

[Ernest314]

Depends on #177 & #271.