Revisit usage of shared instance of TaskService

since TaskTransactionInterceptor is now synchronized to ensure proper persistence handling usage of single instance in multithreading environment is not too efficient. We need to revisit it and look at possible options:

• rely completely on RuntimeManager that always deliver new instance of task service
• separate task operations from task queries
• think about multi tenancy for conole/kie-wb as single instance won't support that

Comments more than welcome