[Qt] New status bar Unit Display Control and related changes.

- New status bar control shows the current Unit of Display.
  When clicked (left,or right button) it shows a context menu
  that allows the user to switch the current Unit of Display (BTC, mBTC, uBTC)
- Recent Requests and Transaction Table headers are now updated when
  unit of display is changed, because their "Amount" column now displays the
  current unit of display.
- Takes care of issue #3970 Units in transaction export csv file.
- Small refactors for reusability.
- Demo Video https://www.youtube.com/watch?v=wwcr0Yh68go&list=UUG3jF2hgofmLWP0tRPisQAQ
- changes after Diapolo's feedback. Have not been able to build after last pool, issues with boost on MacOSX, will test on Ubuntu these changes.
- removed return statement on switch
- renamed onDisplayUnitsChanged(int) to updateDisplayUnit(int)
- now getAmountColumnTitle(int unit) takes a simple unit parameter. moved to BitcoinUnits.

src/qt/bitcoingui.cpp

@@ -28,6 +28,7 @@
 
 #include <iostream>
 
+#include <QAction>
 #include <QApplication>
 #include <QDateTime>
 #include <QDesktopWidget>
@@ -39,6 +40,7 @@
 #include <QMenuBar>
 #include <QMessageBox>
 #include <QMimeData>
+#include <QPoint>
 #include <QProgressBar>
 #include <QProgressDialog>
 #include <QSettings>
@@ -49,6 +51,8 @@
 #include <QToolBar>
 #include <QVBoxLayout>
 
+
+
 #if QT_VERSION < 0x050000
 #include <QUrl>
 #include <QTextDocument>
@@ -156,10 +160,13 @@ BitcoinGUI::BitcoinGUI(bool fIsTestnet, QWidget *parent) :
     QHBoxLayout *frameBlocksLayout = new QHBoxLayout(frameBlocks);
     frameBlocksLayout->setContentsMargins(3,0,3,0);
     frameBlocksLayout->setSpacing(3);
+    unitDisplayControl = new UnitDisplayStatusBarControl();
     labelEncryptionIcon = new QLabel();
     labelConnectionsIcon = new QLabel();
     labelBlocksIcon = new QLabel();
     frameBlocksLayout->addStretch();
+    frameBlocksLayout->addWidget(unitDisplayControl);
+    frameBlocksLayout->addStretch();
     frameBlocksLayout->addWidget(labelEncryptionIcon);
     frameBlocksLayout->addStretch();
     frameBlocksLayout->addWidget(labelConnectionsIcon);
@@ -420,6 +427,8 @@ void BitcoinGUI::setClientModel(ClientModel *clientModel)
             walletFrame->setClientModel(clientModel);
         }
 #endif
+
+        this->unitDisplayControl->setOptionsModel(clientModel->getOptionsModel());
     }
 }
 
@@ -1000,3 +1009,72 @@ void BitcoinGUI::unsubscribeFromCoreSignals()
     // Disconnect signals from client
     uiInterface.ThreadSafeMessageBox.disconnect(boost::bind(ThreadSafeMessageBox, this, _1, _2, _3));
 }
+
+UnitDisplayStatusBarControl::UnitDisplayStatusBarControl():QLabel()
+{
+    optionsModel = 0;
+    createContextMenu();
+    setStyleSheet("font:11pt; color: #333333");
+    setToolTip(tr("Unit to show amounts in. Click to select another unit."));
+}
+
+/** So that it responds to left-button clicks */
+void UnitDisplayStatusBarControl::mousePressEvent(QMouseEvent *event)
+{
+    onDisplayUnitsClicked(event->pos());
+}
+
+/** Creates context menu, its actions, and wires up all the relevant signals for mouse events. */
+void UnitDisplayStatusBarControl::createContextMenu()
+{
+    menu = new QMenu();
+    foreach(BitcoinUnits::Unit u, BitcoinUnits::availableUnits())
+    {
+        QAction *menuAction = new QAction(QString(BitcoinUnits::name(u)), this);
+        menuAction->setData(QVariant(u));
+        menu->addAction(menuAction);
+    }
+    connect(menu,SIGNAL(triggered(QAction*)),this,SLOT(onMenuSelection(QAction*)));
+
+    // what happens on right click.
+    setContextMenuPolicy(Qt::CustomContextMenu);
+    connect(this,SIGNAL(customContextMenuRequested(const QPoint&)),this,SLOT(onDisplayUnitsClicked(const QPoint&)));
+}
+
+/** Lets the control know about the Options Model (and its signals) */
+void UnitDisplayStatusBarControl::setOptionsModel(OptionsModel *optionsModel)
+{
+    if (optionsModel)
+    {
+        this->optionsModel = optionsModel;
+
+        // be aware of a display unit change reported by the OptionsModel object.
+        connect(optionsModel,SIGNAL(displayUnitChanged(int)),this,SLOT(updateDisplayUnit(int)));
+
+        // initialize the display units label with the current value in the model.
+        updateDisplayUnit(optionsModel->getDisplayUnit());
+    }
+}
+
+/** When Display Units are changed on OptionsModel it will refresh the display text of the control on the status bar */
+void UnitDisplayStatusBarControl::updateDisplayUnit(int newUnits)
+{
+    setText(BitcoinUnits::name(newUnits));
+}
+
+/** Shows context menu with Display Unit options by the mouse coordinates */
+void UnitDisplayStatusBarControl::onDisplayUnitsClicked(const QPoint& point)
+{
+    QPoint globalPos = mapToGlobal(point);
+    menu->exec(globalPos);
+}
+
+/** Tells underlying optionsModel to update its current display unit. */
+void UnitDisplayStatusBarControl::onMenuSelection(QAction* action)
+{
+    if (action)
+    {
+        optionsModel->setDisplayUnit(action->data());
+    }
+}
+