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/optionsmodel.cpp

@@ -1,11 +1,12 @@
 #include "optionsmodel.h"
-#include "bitcoinunits.h"
-#include <QSettings>
 
+#include "bitcoinunits.h"
 #include "init.h"
 #include "walletdb.h"
 #include "guiutil.h"
 
+#include <QSettings>
+
 OptionsModel::OptionsModel(QObject *parent) :
     QAbstractListModel(parent)
 {