Move ctfnote setup to config file

[ViRb3]

Not sure about your thoughts on this one, but it makes the bot truly stateless and ctfnote works without any manual configuration even after restart.

[lucidBrot]

I agree that loading the auth from a file is way cleaner. It's something I also though to do, but then never did. ( #5 )
Points to be careful with:

• The bot should still start up correctly even if the ctfnote server is not reachable, failing auth, whatever... . It does not look to me like your changes will have issues with this though.
• For the same reasons, I want to keep the commands to modify the server auth at runtime.

It's always useful to be able to fix the setup even if robin and cyan are asleep.

[RobinJadoul]

Agreed with both sentiments here:

• it's nice to have the default in the config file
• it's nice to have a manual escape hatch to update it
• maybe it's also nice to be able to reload the config from disk to go back to default (maybe as a separate changeset)