Adding the ability to set the QGOSUB variable in the queue configuration page

In the dialplan for queues the variable QGOSUB is included

Queue(9471,${QOPTIONS},,${QAANNOUNCE},${QMAXWAIT},${QAGI},,${QGOSUB},${QRULE},${QPOSITION}) 

Even though this variable is checked  against VQ_GOSUB  

Set(QGOSUB=${IF($[${LEN(${VQ_GOSUB})}>0]?${VQ_GOSUB}:${QGOSUB})})

 there is no way in default freepbx to set this except via some 'custom' dialplan

It would be a trivial addition to add a single text box to the queue page to set this as I documented some years ago https://www.cyber-cottage.co.uk/?p=836 for the qmacro , The idea was rejected at the time by the developers as they said qmacro variable was included in the dialplan, But to this day the setting it is not exposed in the GUI. 

This change is trivial and would add greatly to functionality of queues