Switch editor button, onEditorChange event method & toggleToolbar method.

[trymeouteh]

To create a new button ql-toggle-editor which when pressed will trigger the onEditorChange event method.

The onEventChange method is an event that when triggered is used to switch the editor from a rich text editor to a HTML editor or a markdown editor, etc. The method is used to convert the text inside the editor and the converted text is returned in the method.

And the toggleToolbar method is used to hide all the buttons in the toolbar except for the ql-toggle-editor button.