All service methods that modify backend state now have two versions:
synchronous and asynchronous. This is to make calling `update(...)`
less error prone: previously such call would do nothing unless you
said `service.update(...).execute()`.
Use VersionedId instead of (id, version) pair in service methods.
[java-client] Remove SphereClient and AppClient.

These were of little use until we make the distinction between
'shop' and 'app' clients.
[java-client] Rename ShopClient to SphereClient.
[play-sdk] Merge Sphere and SphereClient.