Standard configuration for bot backends

[wallabra]

A triarc bot currently requires specially written code to manually fetch configuration from wherever before it can connect online. Instead, it should be able to read a standardized configuration file, in a not yet decided format, which specifies multiple backends and their parameters. This may allow triarc.bot to have its own __main__.py.

• Elaborate configuration module, for backend-agnostic configuration file loading
• Add abstract configuration methods, and use supplied configuration fully, for each backend:
  • IRC
  • Discord
  • XMPP
• Use configuration in all examples