1. Make scaling up factor and corner radius of icon can be configured by delegate callback.
2. Add a style of displaying only icon without bottom description label.
3. It's hard to tap corner button on icon cell when editing, so that change image setting method from "setBackgroundImage" to "setImage" then set edge insets for corner button.
4. Fix bug: The scaling up factor of cell calculated wrong when long pressed.
5. Fix bug: Auto-calculated height of draggableView made a mistake.
Make system version check system-irrelevant.
Delete test project. Only keep draggable control.

Keep pure and easy copy.
Demo project will create in another repository.