start consolidating events

[mwdchang]

Summary

Mostly consolidate how events are passed - right now we have a mix of using event-emitters for bubbling up events, and using an event-bus for broadcasting across the Vue-app. This is a legacy architecture when some components were co-located and some where not.

Here we consolidate as much as we can, favouring using the vue-emit rather than the event-bus.
They are kind of the same thing with respect to the designs we have at this stage, but the idea is to pick a single method to make the logic and implementation easier to follow, less error-prone, and to indicate a more de-facto way of handling things rather than having mixed modalities.

TODO: Once this has been achieved we can then further refactor and significantly simplify the vue-templates, and also make things more systematic to add new operators.

Testing

Things should work as before except for Julia-stratify, which is slated to be decommissioned.