Bitcoin-Qt: massive header and cpp cleanup

- try to enforce the same style to all Qt related files
- remove unneeded includes from the files
- add missing Q_OBJECT, QT_BEGIN_NAMESPACE / QT_END_NAMESPACE
- prepares for a pull-req to include Qt5 compatibility

src/qt/bitcoinamountfield.cpp

@@ -1,18 +1,14 @@
 #include "bitcoinamountfield.h"
+
 #include "qvaluecombobox.h"
 #include "bitcoinunits.h"
-
 #include "guiconstants.h"
 
-#include <QLabel>
-#include <QLineEdit>
-#include <QRegExpValidator>
 #include <QHBoxLayout>
 #include <QKeyEvent>
 #include <QDoubleSpinBox>
-#include <QComboBox>
 #include <QApplication>
-#include <qmath.h>
+#include <qmath.h> // for qPow()
 
 BitcoinAmountField::BitcoinAmountField(QWidget *parent):
         QWidget(parent), amount(0), currentUnit(-1)