Adds a few new logging utility classes. One to save to files with a date, one to support optional fields in formats, last to filter partial log messages.
ref: N25B-401
Created a class `BaseAgent`, from which all agents inherit. They get
assigned a logger with a nice name (something like
`control_backend.agents.AgentName`).
The BDI core takes care of its own logger, as bdi is still a module.
ref: N25B-241
