[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,