[Qt] paymentserver: start netManager in uiReady()

- remove explicit init of netManager as this is done in the constructor
  anyway
- move initNetManager() call to uiReady(), which removes an assert() and
  allows us to use message() in initNetManager() (currently unused but
  could be necessary because of proxy related messages)
- make initNetManager() private
- update paymentservertests.cpp

src/qt/paymentserver.h

@@ -77,9 +77,6 @@ public:
     // Return certificate store
     static X509_STORE* getCertStore() { return certStore; }
 
-    // Setup networking
-    void initNetManager();
-
     // Constructor registers this on the parent QApplication to
     // receive QEvent::FileOpen events
     bool eventFilter(QObject *object, QEvent *event);
@@ -117,6 +114,9 @@ private:
     void handleURIOrFile(const QString& s);
     void fetchRequest(const QUrl& url);
 
+    // Setup networking
+    void initNetManager();
+
     bool saveURIs;                      // true during startup
     QLocalServer* uriServer;