[Qt] include and file header cleanup

- alphabetical ordering
- correct ordering own headers before normal headers etc.

src/qt/bitcoinamountfield.h

@@ -7,12 +7,12 @@
 
 #include <QWidget>
 
+class AmountSpinBox;
+
 QT_BEGIN_NAMESPACE
 class QValueComboBox;
 QT_END_NAMESPACE
 
-class AmountSpinBox;
-
 /** Widget for entering bitcoin amounts.
   */
 class BitcoinAmountField: public QWidget