Bug fixes

• Prevented from changing the view document during the render phase. Closes ckeditor/ckeditor5#1530. (7cf835e)
• Fixed memory leaks during editor initialization and destruction (see ckeditor/ckeditor5#1341). (fd18fb9)

Other changes

• The class property should control the DOM class attribute in all UI components. Closes #450. (b9b68c6)
• Updated translations. (b9caee9) (a3afaaa) (909e676)

BREAKING CHANGES

• Upgraded minimal versions of Node to 8.0.0 and npm to 5.7.1. See: ckeditor/ckeditor5#1507. (612ea3c)
• The BallonPanelView#className property was renamed to #class.
• The ToolbarView#className property was renamed to #class.
• The EditableUIView#externalElement property (which held the element on which the editor was created if it was explicitly passed) was removed.
• The EditorUIView#editableElement property was made private. Use editor.ui.getEditableElement() method instead.