Add new API to verify object release

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

.../androidTest/java/org/matrix/olm/OlmGroupSessionTest.java

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

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

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