qt: define QT_NO_KEYWORDS

QT_NO_KEYWORDS prevents Qt from defining the `foreach`, `signals`,
`slots` and `emit` macros.

Avoid overlap between Qt macros and boost - for example #undef hackiness
in #6421.

Conflicts:
	src/qt/addressbookpage.cpp
	src/qt/peertablemodel.cpp
	src/qt/receivecoinsdialog.cpp
	src/qt/rpcconsole.cpp

Rebased-From: d29ec6c2301e593d577126d1ca85b93307b32bf1
Github-Pull: #6433

src/qt/rpcconsole.h

@@ -45,7 +45,7 @@ protected:
     virtual bool eventFilter(QObject* obj, QEvent *event);
     void keyPressEvent(QKeyEvent *);
 
-private slots:
+private Q_SLOTS:
     void on_lineEdit_returnPressed();
     void on_tabWidget_currentChanged(int index);
     /** open the debug.log from the current datadir */
@@ -58,7 +58,7 @@ private slots:
     void showEvent(QShowEvent *event);
     void hideEvent(QHideEvent *event);
 
-public slots:
+public Q_SLOTS:
     void clear();
     void message(int category, const QString &message, bool html = false);
     /** Set number of connections shown in the UI */
@@ -74,7 +74,7 @@ public slots:
     /** Handle updated peer information */
     void peerLayoutChanged();
 
-signals:
+Q_SIGNALS:
     // For RPC command executor
     void stopExecutor();
     void cmdRequest(const QString &command);