Rename "balloon toolbar editor" into "balloon editor"

[wwalc]

I know we had a similar discussion in #402, but let me propose this anyway.

Right now we have three different types of editors:

• Classic editor
• Inline editor
• Balloon toolbar editor

Even if "balloon toolbar editor" tells more precisely what kind of editor it is, IMO is worse than "balloon editor", because:

• It's inconsistent with other names (where toolbar is not mentioned).
• It's longer, making all sentences like "Download balloon toolbar editor build" longer than they should be.
• "Classic"/"Inline" are not meaningful either, because one does not know what "classic" means unless he reads about it and see the demo. So the argumentation about semantic correctness is not that critical imo.
• It's easier to look at the code samples when you see things which are very similar to each other: ClassicEditor.create(), InlineEditor.create(), BalloonEditor.create().
• It could be also easier this way to propose via CDN something like this:

https://cdn.ckeditor.com/ckeditor5/0.11.0/classic/ckeditor.js
https://cdn.ckeditor.com/ckeditor5/0.11.0/inline/ckeditor.js
https://cdn.ckeditor.com/ckeditor5/0.11.0/balloon/ckeditor.js

I know the change will be a bit painful to process, but this is the last moment to eventually do this.