Full support for other units, add configuration option for default unit (used when displaying amounts)

src/qt/qvaluecombobox.cpp

@@ -0,0 +1,27 @@
+#include "qvaluecombobox.h"
+
+QValueComboBox::QValueComboBox(QWidget *parent) :
+        QComboBox(parent), role(Qt::UserRole)
+{
+    connect(this, SIGNAL(currentIndexChanged(int)), this, SLOT(handleSelectionChanged(int)));
+}
+
+int QValueComboBox::value() const
+{
+    return itemData(currentIndex(), role).toInt();
+}
+
+void QValueComboBox::setValue(int value)
+{
+    setCurrentIndex(findData(value, role));
+}
+
+void QValueComboBox::setRole(int role)
+{
+    this->role = role;
+}
+
+void QValueComboBox::handleSelectionChanged(int idx)
+{
+    emit valueChanged();
+}