refactor(src/index.ts): shortening more code
refactor(src/index.ts): shortening more code

- refactors a number of functions; reducing their size by 1/2
- refactors to allow for proper testing memoization
- updates the following functions
  - `getUniqueId`
  - `getDeviceId`
  - `getModel`
  - `getBrand`
  - `getSystemVersion`
  - `getBundleId`
  - `getApplicationName`
  - `getBuildNumber`
  - `getVersion`
  - `isTablet`
  - `getDeviceType`
  - `getDeviceTypeSync`

rebeccahughes/react-native-device-info,rebeccahughes/react-native-device-info,rebeccahughes/react-native-device-info,rebeccahughes/react-native-device-info,rebeccahughes/react-native-device-info,rebeccahughes/react-native-device-info