[futures] Add Play-speficic Requests.
Merge branch 'master' into futures
[futures] Play-specific services.
Use Play Promises in SphereClient and CurrentCustomer,
unify exception handling, call API mode "sphere.products.mode".
Merge branch 'master' into futures

Conflicts:
	java-client/src/test/scala/shop/CustomerServiceSpec.scala
Fix test after merge.
Merge branch 'master' into futures

Conflicts:
	java-client/src/main/java/io/sphere/client/shop/model/CustomerUpdate.java
	java-client/src/test/scala/shop/CustomerServiceSpec.scala
	play-sdk/app/sphere/SphereClient.java
[futures] Adapt to Gregor's changes.
[futures] Use Play Promises in CurrentCart and CurrentCustomer.