#414 Update docu and javadoc

...rc/main/java/de/fitko/fitconnect/api/services/Sender.java

...ain/java/de/fitko/fitconnect/api/services/Subscriber.java

...a/de/fitko/fitconnect/api/services/auth/OAuthService.java

...e/fitko/fitconnect/api/services/crypto/CryptoService.java

...connect/api/services/validation/CertificateValidator.java

...fitconnect/api/services/validation/MetadataValidator.java

client/README.md

...ain/java/de/fitko/fitconnect/client/SubscriberClient.java

...n/java/de/fitko/fitconnect/core/SubmissionSubscriber.java