Change text commands to slash commands

[NotMyLyfe]

Change text commands to slash commands (#69)

• Refactor app for discord.py 2.0 and update dependencies
• Modify each text command to slash commands
• Update documentation to include slash commands

[Kav-K]

Hey are you sure you want to continue with this? I personally consider UWHelperBot a dead project (a stable one though) that won’t be really maintained after this term, you might find it more fulfilling to contribute to GPT3Discord instead, nevertheless I very much appreciate the effort