Move ProgramErrorAppender to logger.

Add a JUnit rule for using JimFS.

This means each test doesn't have to set it up and tear it down
manually (although only one actually did bother to tear it down :)).

Move update applying into the file handler.

Add a README.

Kick off some basic dev info by documenting the new error handling.

SLF4J Logging in the core.

Slf4j logging a few more things.

Change a couple of event bus error reportings.

Remove some more AppErrorEvents.

Remove some more AppErrorEvents.

Slf4j a few more bits.

Remove CallbackNotFoundException, tidy up Query.

Add logback to licences

Use slf4j for a few errors.

We don't need to reregister on nick change now, as we get all
the events anyway and filter them manually.

Make existing Log.error calls use app/user markers.

Initial work on logback logging.

Remove silly URL usage in PluginMetaData.

Split out a PluginFileHandler.

Minor tidying in plugins

Remove profile migration logic.

The "old" profiles were pre 0.6.3m1 - if anyone upgrades from that
long ago they'll just lose their profiles.

Fix ServerManager logic for disconnected servers.