switch enhancements - Add more switch types

[jahnli]

This function solves the problem (这个功能解决的问题)

Improve functions and enhance user experience

Expected API (期望的 API)

1.Add more switch types (circle 、round 、line )
2.Customize the icon displayed on the switch button.

[07akioni]

Maybe we will provide a square switch like iOS4, infact I've tried before but not done.

line typed switch won't be provided. It's just useless.