t/95: Remove the Controller class

[oleq]

Closes ckeditor/ckeditor5#5266.

[pjasiun]

I remember we talked about View taking attributes object as a second parameter, so one can easily initialize multiple observable creating a view class. I'm not sure do we need to make it generic, so should such parameter be in the base View class or in specific views, if needed.

[Reinmar]

The PRs to review:

• this one
• t/103: Update components once UI architecture has been stripped of Controller class ckeditor5-ui-default#104
• t/38: Updated Lark after the removal of Controller class. ckeditor5-theme-lark#39
• t/34: Refactoring in ClassicEditor classes and tests. ckeditor5-editor-classic#35
• t/38: Adapt ClassicTestEditor to Controller–less architecture ckeditor5-core#39
• Updated UI components after UI architecture refactoring. ckeditor5-list#21
• Updated basic styles classes after the removal of Controller class. ckeditor5-basic-styles#32
• t/41: Updated heading after the removal of Controller class. ckeditor5-heading#42
• t/45: Updated undo after the removal of Controller class. ckeditor5-undo#46
• Refactoring after UI architecture refactoring ckeditor5-link#58
• manual tests pass
• automated tests pass

[Reinmar]

I decided to merge all this code to master and review it there because we risk having too many conflicts too quickly and blocking ourselves. 3 of you worked on these changes, all tests pass, CC is 100%, so let's not keep the world (:D) waiting.

[Reinmar]

I finished the review. I haven't found many things, which is great taken the size of the refactoring. I wrote down everything in https://github.com/ckeditor/ckeditor5-ui/issues/103.

Kudos guys!