Update state machine

- Split INITIALIZING state into Init+Bind+Connect
 - Remove PAUSE state
 - Convert state/transitions to enum classes (CamelCase)
 - Transition to a state only once previous handler is complete
 - Add CompleteInit transition to notify Initializing state
   that config updates are complete
 - Deprecate WaitForEndOfState(transition) in favor of
   WaitForState(state)/WaitForNextState()
 - Update tests/plugins to new APIs
 - Deprecate CheckCurrentState() in favor of NewStatePending()

test/helper/devices/TestPollOut.h

@@ -22,7 +22,7 @@ namespace test
 class PollOut : public FairMQDevice
 {
   protected:
-    auto Init() -> void override
+    auto InitTask() -> void override
     {
         std::this_thread::sleep_for(std::chrono::milliseconds(200));
     }