Prevent window from being shown momentarily when using -min

- In a previous patch, show() was added to all the page switcher functions. As the contructor calls showOverviewPage(), this means the window is shown in the constructor.
- This change prevents this by connecting show() to the signal instead.

src/qt/bitcoingui.cpp

@@ -191,10 +191,15 @@ void BitcoinGUI::createActions()
     sendCoinsAction->setShortcut(QKeySequence(Qt::ALT + Qt::Key_2));
     tabGroup->addAction(sendCoinsAction);
 
+    connect(overviewAction, SIGNAL(triggered()), this, SLOT(show()));
     connect(overviewAction, SIGNAL(triggered()), this, SLOT(gotoOverviewPage()));
+    connect(historyAction, SIGNAL(triggered()), this, SLOT(show()));
     connect(historyAction, SIGNAL(triggered()), this, SLOT(gotoHistoryPage()));
+    connect(addressBookAction, SIGNAL(triggered()), this, SLOT(show()));
     connect(addressBookAction, SIGNAL(triggered()), this, SLOT(gotoAddressBookPage()));
+    connect(receiveCoinsAction, SIGNAL(triggered()), this, SLOT(show()));
     connect(receiveCoinsAction, SIGNAL(triggered()), this, SLOT(gotoReceiveCoinsPage()));
+    connect(sendCoinsAction, SIGNAL(triggered()), this, SLOT(show()));
     connect(sendCoinsAction, SIGNAL(triggered()), this, SLOT(gotoSendCoinsPage()));
 
     quitAction = new QAction(QIcon(":/icons/quit"), tr("E&xit"), this);
@@ -563,7 +568,6 @@ void BitcoinGUI::incomingTransaction(const QModelIndex & parent, int start, int
 
 void BitcoinGUI::gotoOverviewPage()
 {
-    show();
     overviewAction->setChecked(true);
     centralWidget->setCurrentWidget(overviewPage);
 
@@ -573,7 +577,6 @@ void BitcoinGUI::gotoOverviewPage()
 
 void BitcoinGUI::gotoHistoryPage()
 {
-    show();
     historyAction->setChecked(true);
     centralWidget->setCurrentWidget(transactionsPage);
 
@@ -584,7 +587,6 @@ void BitcoinGUI::gotoHistoryPage()
 
 void BitcoinGUI::gotoAddressBookPage()
 {
-    show();
     addressBookAction->setChecked(true);
     centralWidget->setCurrentWidget(addressBookPage);
 
@@ -595,7 +597,6 @@ void BitcoinGUI::gotoAddressBookPage()
 
 void BitcoinGUI::gotoReceiveCoinsPage()
 {
-    show();
     receiveCoinsAction->setChecked(true);
     centralWidget->setCurrentWidget(receiveCoinsPage);
 
@@ -606,7 +607,6 @@ void BitcoinGUI::gotoReceiveCoinsPage()
 
 void BitcoinGUI::gotoSendCoinsPage()
 {
-    show();
     sendCoinsAction->setChecked(true);
     centralWidget->setCurrentWidget(sendCoinsPage);