qt: add network-specific style object

Mainly cleanups: Gets rid of isTestNet everywhere, by keeping track
of network-specific theming in a central place.

Also makes GUI no longer dependent on the network ID enumeration, which
alleviates concerns about #4802.

src/qt/bitcoingui.h

@@ -19,6 +19,7 @@
 #include <QSystemTrayIcon>
 
 class ClientModel;
+class NetworkStyle;
 class Notificator;
 class OptionsModel;
 class RPCConsole;
@@ -46,7 +47,7 @@ class BitcoinGUI : public QMainWindow
 public:
     static const QString DEFAULT_WALLET;
 
-    explicit BitcoinGUI(bool fIsTestnet = false, QWidget *parent = 0);
+    explicit BitcoinGUI(const NetworkStyle *networkStyle, QWidget *parent = 0);
     ~BitcoinGUI();
 
     /** Set the client model.
@@ -114,13 +115,13 @@ private:
     int spinnerFrame;
 
     /** Create the main UI actions. */
-    void createActions(bool fIsTestnet);
+    void createActions(const NetworkStyle *networkStyle);
     /** Create the menu bar and sub-menus. */
     void createMenuBar();
     /** Create the toolbars */
     void createToolBars();
     /** Create system tray icon and notification */
-    void createTrayIcon(bool fIsTestnet);
+    void createTrayIcon(const NetworkStyle *networkStyle);
     /** Create system tray menu (or setup the dock menu) */
     void createTrayIconMenu();