Added RNFS and refactor image upload to use it

mobile/ios/Podfile

@@ -35,6 +35,8 @@ target 'DeightonAR' do
   pod 'ViroKit', :path => '../node_modules/react-viro/ios/dist/ViroRenderer/'
 
   pod 'react-native-image-picker', :path => '../node_modules/react-native-image-picker'
+
+  pod 'RNFS', :path => '../node_modules/react-native-fs'
 end
 
 # See https://gist.github.com/Jpunt/3fe75effd54a702034b75ff697e47578