introduce bitcoin amount field with split amount/decimals, to protect against mistakes (https://forum.bitcoin.org/index.php?topic=19168.0)

src/qt/bitcoinamountfield.cpp

@@ -0,0 +1,67 @@
+#include "bitcoinamountfield.h"
+
+#include <QLabel>
+#include <QLineEdit>
+#include <QRegExpValidator>
+#include <QHBoxLayout>
+#include <QKeyEvent>
+
+BitcoinAmountField::BitcoinAmountField(QWidget *parent):
+        QWidget(parent), amount(0), decimals(0)
+{
+    amount = new QLineEdit(this);
+    amount->setValidator(new QRegExpValidator(QRegExp("[0-9]+"), this));
+    amount->setAlignment(Qt::AlignRight|Qt::AlignVCenter);
+    amount->installEventFilter(this);
+    amount->setMaximumWidth(80);
+    decimals = new QLineEdit(this);
+    decimals->setValidator(new QRegExpValidator(QRegExp("[0-9]+"), this));
+    decimals->setMaxLength(8);
+    decimals->setAlignment(Qt::AlignLeft|Qt::AlignVCenter);
+    decimals->setMaximumWidth(75);
+
+    QHBoxLayout *layout = new QHBoxLayout(this);
+    layout->setSpacing(0);
+    layout->addWidget(amount);
+    layout->addWidget(new QLabel(QString(".")));
+    layout->addWidget(decimals);
+    layout->addStretch(1);
+
+    setFocusPolicy(Qt::TabFocus);
+    setLayout(layout);
+    setFocusProxy(amount);
+
+    // If one if the widgets changes, the combined content changes as well
+    connect(amount, SIGNAL(textChanged(QString)), this, SIGNAL(textChanged()));
+    connect(decimals, SIGNAL(textChanged(QString)), this, SIGNAL(textChanged()));
+}
+
+void BitcoinAmountField::setText(const QString &text)
+{
+    const QStringList parts = text.split(QString("."));
+    if(parts.size() == 2)
+    {
+        amount->setText(parts[0]);
+        decimals->setText(parts[1]);
+    }
+}
+
+QString BitcoinAmountField::text() const
+{
+    return amount->text() + QString(".") + decimals->text();
+}
+
+// Intercept '.' and ',' keys, if pressed focus a specified widget
+bool BitcoinAmountField::eventFilter(QObject *object, QEvent *event)
+{
+    Q_UNUSED(object);
+    if(event->type() == QEvent::KeyPress)
+    {
+        QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
+        if(keyEvent->key() == Qt::Key_Period || keyEvent->key() == Qt::Key_Comma)
+        {
+            decimals->setFocus();
+        }
+    }
+    return false;
+}