Move PluginCollection and Plugin to utils

[pjasiun]

What Plugin/PluginCollection are, is the util to solve problems with the dependencies tree. It's enough to rename editor variable to context and change docs to make it more flexible util. It's very helpful to split a project into pieces, event if it is editor-independent.

Note that it's possible to make it compatible with the editors plugins:

export default class Plugin {
	constructor( contex ) {
		_.extend( this, contex );
	}

	// ...
}

export default class Editor {
	constructor( config ) {
		this.plugins = new PluginCollection( { editor: this } );

		// ...
	}

	// ...
}

[pjasiun]

Also, I think it would be a good change in general. A class should do one task. This class has a task to solve dependencies and it is what it really do. Making it a util lets developers understand it easier.

[Reinmar]

Makes sense. Then Plugin will need to become a util as well :D But in fact, I was rather planning to make Plugin an interface, so we could do both things at the same time. Although, the latter is a bigger change, unfortunately.

Related ticket: https://github.com/ckeditor/ckeditor5-core/issues/54.

[Reinmar]

But I don't like this for CKEditor:

_.extend( this, contex );

We should keep the editor param (so the ctx of Editor#plugins will be the editor itself). Then, in the plugins we'll do this:

constructor( editor ) {
    this.editor = editor;
}

[Reinmar]

This should be handled together with https://github.com/ckeditor/ckeditor5-core/issues/78.

[Reinmar]

BTW, soon we'll make commands and command collection utils too and ckeditor5-core will become a set of utils and interfaces (cause editor will be an interface too).

[Reinmar]

Closing due to lack of interest in this now.