Bug fixes

• Fixed memory leaks during editor initialization and destruction. Created helpers for testing memory usage. Closes ckeditor/ckeditor5#1341. (11ca135)

Other changes

• Editor UI classes API refactoring. See breaking changes. Closes ckeditor/ckeditor5#1449. (aca1ff1)
• Remove editor#pluginsReady event. Closes ckeditor/ckeditor5#1477. (6d63538)
• The Editor#getData() method now accepts options.trim parameter. By default it will now return an empty string when the editor is empty (instead of returning '<p>&nbsp;</p>' as before). (4f8abd1)
• Throw an error from editor.plugins.get() if the plugin is not loaded. Closes #148. (a56b47a)
• Updated translations. (4cf6f4f) (a8367a5) (0e09317)

BREAKING CHANGES

• Upgraded minimal versions of Node to 8.0.0 and npm to 5.7.1. See: ckeditor/ckeditor5#1507. (612ea3c)
• The Editor#getData() method now returns an empty string by default when editor content is empty (instead of returning '<p>&nbsp;</p>' as before).
• The editor#pluginsReady event was removed. Use plugin afterInit() method instead.
• Removed EditorWithUI#element property. The EditorUI#element property should be used instead.
• Removed EditorWithUI#uiReady event. The EditorUI#ready event should be used instead.
• Removed view parameter in EditorUI constructor. Only subclasses should use it without passing it further to EditorUI.
• Removed EditorUI#view property. The view property from subclasses (like ClassicEditorUI#view) should be used directly instead.
• The editor.plugins.get() will now throw an error if the plugin is not loaded. Use editor.plugins.has() to check if plugin is available.