introduce slash commands

[abe-101]

slash commands allow for more easy to use interactions with the bot
pressing / will bring up a context menu with commands the bot can do

Things to do:

• set up cogs
• move new_chapter to cogs and make a hybrid commnand
• create a delete_chapter that reverse the new_chapter command

cog in the framework discord.py is like an extension basically a folder called cog and within the folder you can have different "extensions" that can be loaded into the bot
for all intent and purposes it's a way to break apart the code out of a single main file