Dockerize

[ThisIsntTheWay]

This PR dockerizes the bot.
Not only will this make the bot more portable, it will also ensure that the bot restarts in case of mishaps/reboots.

Additionally, some potentially major changes have been made:

• Added Kotoba user ID, channel ID to env var.
  • I feel like hard coding such things is not the best thing to do.
• Added warning if DB is missing.
• Moved source code to /src, renamed entrypoint to main.py.
  • This is just to make everything a bit more organized.