Phases API in BaseRunModel should be events

[jondequinor]

For an outside observer, looking at a running BaseRunModel (i.e. the CLI or the GUI), the phases change without the observer ever knowing that it did. So polling is the only way of knowing in what phase some BaseRunModel is at any point in time. Which is bad (e.g. you poll every 1 second, phases changes multiple times within that second—information is lost).

Principally, temporal information should not be stored as mutable data on a shared object.

This is obviously a case that should be solved using a publish/subscribe type programming pattern. Everytime a BaseRunModel derived model (ESMDA, Smoother, etc), changes the phase, it should simply emit an event that the CLI/GUI subscribe to.

[jondequinor]

This is most likely going to be a fundamental design goal of #1250 so we can just close this. (AS LONG AS IT IS NOT FORGOTTEN)