Fix breaking changes in React Native 0.47

[fractalwrench]

This fixes the following issues I found in RN 0.47 (RC 4):

• createJSModules method removed from ReactPackage (removing the override annotation stops the compiler errors and should support older RN versions).
• Fix iOS build by disabling build parallelization, and ensuring that the React target is built before the example project.
• Update visibility of getUseDeveloperSupport method.
• Use react-native-deprecated-custom-components package to get the Navigator working again (we may want to move over to something like react-navigation in future).
• Submit PR to react-native-vector-icons package as the library is also affected by the removal of createJSModules.