refactor to more idiomatic RAII

* FairMQTransportFactoryZMQ: move the config invariant
    initialization to ctor
  * FairMQChannel: add new ctor that creates usable channel
  * FairMQSocket*: close sockets in dtor
  * FairMQTransportFactory*: terminate context in dtor
  * FairMQChannel: add Bind/Connect facades (for explicit control, e.g. timing)

fairmq/zeromq/FairMQSocketZMQ.cxx

@@ -565,4 +565,5 @@ int FairMQSocketZMQ::GetConstant(const string& constant)
 
 FairMQSocketZMQ::~FairMQSocketZMQ()
 {
+    Close();
 }