判断是否有权限访问相机，相册，定位

http://www.aslibra.com/blog/read.php/1781.htm

http://www.2cto.com/kf/201405/304909.html

http://stackoverflow.com/questions/18930436/ios-7-uiimagepickercontroller-camera-no-image

http://stackoverflow.com/questions/26070393/is-there-a-way-to-ask-user-for-camera-access-after-they-have-already-denied-it-o/26070594#26070594