GModel support

[Riccardo Mottola]

Hi,

with the last and only known application, Cenon, now being essentially a 
Mac port, we don't need GModels anymore.

What do you think of not building it by default anymore and making a 
bundle so that Gorm can read them and save them to proper gorm files?

I remember Gregory itched more than once about that now incomplete gui 
file format (even if it has sometimes better things than Gorm)

Riccardo