The digital clock of GNOME I am referring to is indicated in this screenshot:This is the advanced custom format I would like GNOME's digital clock to have:%l:%M:%S %p %A, %e %B %Yat the moment this format would be:1:05:10 pm Saturday, 26 December 2015if to get this custom format I would need to install an extra extension, I am willing to, please just tell me the name of the extension I would need and how to install it. 
How do I adjust the format of GNOME's digital clock to an advanced custom format?
gnome;clock;gnome panel