Add code style setting "don't use Qt keywords"

Add a setting to code style that turns off the use of Qt keywords like "slots" and "signals". This setting is then taken into account when generating a new class using the "new class" dialog.

So when "don't use Qt keywords" is enabled, a new class will use "Q_SIGNALS:", and when it is disabled, a new class will use "signals:".

Or have it the other way around and call it "use Qt keywords" if negative checkboxes are to be avoided.