Simplify the serialization / deserializtion methods (CommonSerializeUtils)

...k/src/androidTest/java/org/matrix/olm/OlmSessionTest.java

...dk/src/main/java/org/matrix/olm/CommonSerializeUtils.java

...bSdk/olm-sdk/src/main/java/org/matrix/olm/OlmAccount.java

.../src/main/java/org/matrix/olm/OlmInboundGroupSession.java

...src/main/java/org/matrix/olm/OlmOutboundGroupSession.java

...bSdk/olm-sdk/src/main/java/org/matrix/olm/OlmSession.java

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.cpp

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_account.h

...LibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.cpp

...lmLibSdk/olm-sdk/src/main/jni/olm_inbound_group_session.h

...ibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.cpp

...mLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.h

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.cpp

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_session.h