Create a Plugin manager

[adierkens]

Often times with the tapable interface used projects, they are paired with a set of plugins.

By default we typically just construct a list of them, and apply() them onto the main entry to the library:

class MyThing {
  constructor(conf: { plugins: Array<Plugin> }) {
     conf.plugins.forEach(p => p.apply(this));
  }
}

This works fine for most use-cases, but as projects grow there are often needs for plugins to communicate with each other. It would be helpful to create a manager that handles all of the register, find, applyTo calls for a set of plugins and be able to reuse that across multiple projects.