Make Beaker able to log more to metrics

Please note that this change is mostly a preparation work to make beaker 'ready'. The tracking provider services(e.g. [GA](https://github.com/twosigma/beaker-notebook/blob/alee/metrics/core/src/main/web/plugin/init/track.js#L41)) haven't really be been turned on, meaning upon receiving new events to log the service will ignore them and do nothing. As for really changing the tracking services, #360 has been logged for further discussion.

We should also discuss what are still left to do for v0.55 milestone.