Client Wrapper: avoid possible memory leak on subcription on client clear/disconnect

Description

When SOPC_ClientConfigHelper_Clear is called, if there are some remaining active connections those are automatically disconnected. But if a subscription was active on those connections, the corresponding SOPC_ClientHelper_Subscription* memory is not freed and leads to memory leak and the subscription was not properly deleted prior to connection closure.

Implementation

Client connection should keep track of the allocated SOPC_ClientHelper_Subscription* and should delete the subscription during SOPC_ClientHelperNew_Disconnect call if it was not done by application.

Note: the application shall not use the SOPC_ClientHelper_Subscription* pointer as it is freed after disconnection.