refactor plugin + worker interface

[shanejonas]

this changes the interface names to not have worker in them, also changes the interface to them as to not require workerId, but use the pluginName instead.

It establishes a ExecutionEnvironmentService interface for other Execution Environment Services to follow and used in the PluginController to be able to swap out execution environments.

It also renames WorkerController to WebWorkerExecutionEnvironmentService which implements ExecutionEnvironmentService.

[rekmarks]

This is a great start!

I have a couple of significant change requests that I left and explain inline.

In addition to those, I think it's worth considering how the current execution environment (EE) service interface will work when we have multiple EEs. Ideally, there should be a single EE service class that's capable of starting a plugin in any conceivable EE. In that paradigm, the worker EE service would be a sub-service of that uber-EE service. As I mention inline, I believe that some of the existing public methods of the service interface are too low-level for the plugin controller, but they would be completely appropriate for a class that manages multiple EE services.

[rekmarks]

Looks great! Just a couple of things to iron out.

[rekmarks]

LGTM! There are a couple of pre-existing issues I noticed during review that can be addressed during a follow-up.