[IMP] add field active on crm.case.categ

Hello, 

This PR adds the field 'Active' on the object 'crm.case.categ'. 

Categs are created with xml data (in modules crm, crm_claim, ...) so we can't delete them if we don't use them. Indeed, if we delete  a categ, at the update of the module that creates it, the categ is created again.

With the field active we can unactivate the unused categs.

Best regards,
Actually just setting the default of active to True is sufficient, no need of lambda. By the way boolean fields expect a boolean value (1 will work but is not totally correct).