Refactored file id retrieval methods.
Refactored file id retrieval methods.

All methods that retrieve a file id from Drive now call getDriveFileId.

Also added basic error codes.

hgl888/mobile-chrome-apps,hgl888/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,hgl888/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,wudkj/mobile-chrome-apps,chirilo/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,guozanhua/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,guozanhua/mobile-chrome-apps,hgl888/mobile-chrome-apps,chirilo/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,wudkj/mobile-chrome-apps,wudkj/mobile-chrome-apps,guozanhua/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,hgl888/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,hgl888/mobile-chrome-apps,liqingzhu/mobile-chrome-apps,chirilo/mobile-chrome-apps,chirilo/mobile-chrome-apps,wudkj/mobile-chrome-apps,xiaoyanit/mobile-chrome-apps,hgl888/mobile-chrome-apps,MobileChromeApps/mobile-chrome-apps,guozanhua/mobile-chrome-apps