Flutter使用自定义的Icon

[fancylou]

http://www.muliba.net/flutter/2019/03/29/Flutter%E4%BD%BF%E7%94%A8%E8%87%AA%E5%AE%9A%E4%B9%89%E7%9A%84Icon.html

Flutter默认开启了uses-material-design。