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/qvaluecombobox.h

@@ -8,7 +8,9 @@
 class QValueComboBox : public QComboBox
 {
     Q_OBJECT
+
     Q_PROPERTY(QVariant value READ value WRITE setValue NOTIFY valueChanged USER true)
+
 public:
     explicit QValueComboBox(QWidget *parent = 0);
 
@@ -21,8 +23,6 @@ public:
 signals:
     void valueChanged();
 
-public slots:
-
 private:
     int role;