Make logs available via REST

[ErikBjare]

Logs for each agent (and all agents) should be made available via REST. In the future WebSockets might be used instead.

This is done by creating a log handler that writes to buffers which can then be fetched from REST (probably done by subclassing NullHandler but unsure).

The first version can simply make the entire log available via REST and not support specifying the log of a particular agent.

[ErikBjare]

We did something similar for Homebrain, migrate core functionality to a new module and have the two projects share it.