Add versioning on both Android and iOS. Asynchronous delete when updating version. Refactor mainly on Android.
Revert file mode.
Android changes according to review. Handle error with exception and return error callback in JS. Rename updateAssetsVersion to upgradeAssets.
Merge pull request #1 from jrouault/feature/versioningStep1

Add versioning on both Android and iOS. Asynchronous delete when updating version.