Port modules from bots

[MarkKoz]

Let's discuss what should be ported over. Here is what I have thought of so far:

• Extension management
• Ping command
• Source command (Moving Converters and the Source Cog into botcore #46)
• Help command
• Internal eval (snekbox wrapper #30 ?)
  • Including paste service utilities
  • Base class for use with eval-like cogs (snekbox, internal eval, latex)
• Error handlers
• Logging utils

[camcaswell]

+1 on Help

[ChrisLovering]

we can move the startup greeting to bot-core too, since all our bots do the same thing, but in different ways

https://github.com/python-discord/bot/blob/main/bot/exts/backend/logging.py#L20