basicButton Atto plugin example

This example plugin contains the minimal structure for an Atto plugin using addBasicButton method.

Useful links

• Shifter doc: https://docs.moodle.org/dev/YUI/Shifter
• YUI doc: https://docs.moodle.org/dev/YUI/Modules
• Atto doc: https://docs.moodle.org/dev/Atto
• Editor API: https://apidocs.moodle.org/js/master/classes/M.editor_atto.Editor.html