update CClientUIInterface and remove orphan Wx stuff

- fix ThreadSafeMessageBox always displays error icon
- allow to specify MSG_ERROR / MSG_WARNING or MSG_INFORMATION without a
  custom caption / title
- allow to specify CClientUIInterface::ICON_ERROR / ICON_WARNING and
  ICON_INFORMATION (which is default) as message box icon
- remove CClientUIInterface::OK from ThreadSafeMessageBox-calls, as
  the OK button will be set as default, if none is specified
- prepend "Bitcoin - " to used captions
- rename BitcoinGUI::error() -> BitcoinGUI::message() and add function
  documentation
- change all style parameters and enum flags to unsigned
- update code to use that new API

- update Client- and WalletModel to use new BitcoinGUI::message() and
  rename the classes error() method into message()
- include the possibility to supply the wanted icon for messages from
  Client- and WalletModel via "style" parameter

src/qt/bitcoin.cpp

@@ -7,7 +7,6 @@
 #include "optionsmodel.h"
 #include "guiutil.h"
 #include "guiconstants.h"
-
 #include "init.h"
 #include "ui_interface.h"
 #include "qtipcserver.h"
@@ -35,18 +34,19 @@ Q_IMPORT_PLUGIN(qtaccessiblewidgets)
 static BitcoinGUI *guiref;
 static QSplashScreen *splashref;
 
-static void ThreadSafeMessageBox(const std::string& message, const std::string& caption, int style)
+static void ThreadSafeMessageBox(const std::string& message, const std::string& caption, unsigned int style)
 {
     // Message from network thread
     if(guiref)
     {
         bool modal = (style & CClientUIInterface::MODAL);
-        // in case of modal message, use blocking connection to wait for user to click OK
-        QMetaObject::invokeMethod(guiref, "error",
+        // In case of modal message, use blocking connection to wait for user to click a button
+        QMetaObject::invokeMethod(guiref, "message",
                                    modal ? GUIUtil::blockingGUIThreadConnection() : Qt::QueuedConnection,
                                    Q_ARG(QString, QString::fromStdString(caption)),
                                    Q_ARG(QString, QString::fromStdString(message)),
-                                   Q_ARG(bool, modal));
+                                   Q_ARG(bool, modal),
+                                   Q_ARG(unsigned int, style));
     }
     else
     {