Complete logging support

[tspooner]

We have some logging utilities but they are very skin-deep. We need to be able to pass loggers in a structured manner through to the various components of the experiment, such as the agent, function approximator, domain, etc etc...

In addition to the obvious, this would also be useful to warn users if using agents that have specific unenforced requirements. For example, GreedyGQ requires a stationary behaviour policy but we allow the user to pass any policy type.