Add option to avoid writing extension methods categorized with asterisk prefix

[eMaringolo]

Monticello defined a pattern to define extensions methods by naming them *PackageName, such categories were recognized by package managers and then defined such methods in the package named PackageName instead of the package where the class was defined.

Both VAST and Tonel support first class extension methods, so there is no need to fileout classes with such category name.

The request is to add an option to TonelWriter to use the default category (or none) to the category property (besides the existing vaCategories).