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/transactionview.h

@@ -83,7 +83,7 @@ private:
 
     bool eventFilter(QObject *obj, QEvent *event);
 
-private slots:
+private Q_SLOTS:
     void contextualMenu(const QPoint &);
     void dateRangeChanged();
     void showDetails();
@@ -95,13 +95,13 @@ private slots:
     void openThirdPartyTxUrl(QString url);
     void updateWatchOnlyColumn(bool fHaveWatchOnly);
 
-signals:
+Q_SIGNALS:
     void doubleClicked(const QModelIndex&);
 
     /**  Fired when a message should be reported to the user */
     void message(const QString &title, const QString &message, unsigned int style);
 
-public slots:
+public Q_SLOTS:
     void chooseDate(int idx);
     void chooseType(int idx);
     void chooseWatchonly(int idx);