Change EditableObject's implementation with `fabric.util.createClass`

[swimmingkiim]

Background

I got this idea when I was trying to implement the select method in EditableObject.
The issue that I was facing was that I could not extract EditableObject instances from the JSON format snapshot that the Data class has. In the current project's structure, It's too complicated to handle two states that represent the same thing.

Suggestion

• Implement EditableObject with fabric.util.createClass
• Also implement other custom object classes with EditableObject with fabric.util.createClass

References

• http://fabricjs.com/fabric-intro-part-3