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

src/qt/bitcoinamountfield.h

@@ -0,0 +1,33 @@
+#ifndef BITCOINFIELD_H
+#define BITCOINFIELD_H
+
+#include <QWidget>
+
+QT_BEGIN_NAMESPACE
+class QLineEdit;
+QT_END_NAMESPACE
+
+class BitcoinAmountField: public QWidget
+{
+    Q_OBJECT
+    Q_PROPERTY(QString text READ text WRITE setText NOTIFY textChanged USER true);
+public:
+    explicit BitcoinAmountField(QWidget *parent = 0);
+
+    void setText(const QString &text);
+    QString text() const;
+
+signals:
+    void textChanged();
+
+protected:
+    // Intercept '.' and ',' keys, if pressed focus a specified widget
+    bool eventFilter(QObject *object, QEvent *event);
+
+private:
+    QLineEdit *amount;
+    QLineEdit *decimals;
+};
+
+
+#endif // BITCOINFIELD_H