Sync events between plugins and the websocket connection

[askmike]

Gekko has a plugin system that allows different "plugins" (modules) to communicate between each other via plugin events, see here: https://gekko.wizb.it/docs/extending/add_a_plugin.html#What-kind-of-events-can-I-listen-to- (system 1)

However the UI uses a different event system (over websockeets) to sync the UI state with what is happening internally inside different Gekko instances, see here: https://github.com/askmike/gekko/blob/develop/core/cp.js (system 2)

System 1 is very old and outdated, we need to update and extend system 1 and get rid of system 2.

[askmike]

Closing this in favor of the WIP PR in #1850.