Improve GTK interface by PabloCastellano

GtkClient.py
Improve GTK interface by PabloCastellano

https://github.com/PabloCastellano/yowsup/blob/a2c5b095d0fc139d28485b703a7d3ed040528230/src/Examples/GtkClient.py
https://github.com/PabloCastellano/yowsup/commit/a2c5b095d0fc139d28485b703a7d3ed040528230