Remove compile time transport interface switch

- Remove the compile time check of the transport implementation.
  The transport (zeromq/nanomsg) can be chosen at run time with:
  `device.SetTransport("zeromq"); // possible values are "zeromq" and "nanomsg"`.

  For devices that use FairMQProgOptions, the transport can be configured via cmd option:
  `--transport zeromq` or `--transport nanomsg`. Default values is "zeromq".
  The device receives the configured value with:
  `device.SetTransport(config.GetValue<std::string>("transport"));`

  Old method of setting transport still works. But the NANOMSG constant is not defined.

- Remove old `fairmq/prototest` directory. It was only used as a test for protobuf.
  The protobuf part of Tutorial3 does the same (with different values).

- Fix a bug in FairMQPollerNN, where the `revents` value was not initialized.
  This caused the `poller->CheckOutput()` to trigger when it should not.

fairmq/FairMQDevice.h

@@ -102,9 +102,12 @@ class FairMQDevice : public FairMQStateMachine, public FairMQConfigurable
     /// Print all properties of this and the parent class to LOG(INFO)
     virtual void ListProperties();
 
-    /// Configures the device with a transport factory
+    /// Configures the device with a transport factory (DEPRECATED)
     /// @param factory  Pointer to the transport factory object
-    virtual void SetTransport(FairMQTransportFactory* factory);
+    void SetTransport(FairMQTransportFactory* factory);
+    /// Configures the device with a transport factory
+    /// @param transport  Transport string ("zeromq"/"nanomsg")
+    void SetTransport(const std::string& transport = "zeromq");
 
     /// Implements the sort algorithm used in SortChannel()
     /// @param lhs Right hand side value for comparison