MantisBT should have Custom Fields per Category

i.e.
CATEGORY "Hardware" should require specific data about hardware (CPU, RAM, etc)
CATEGORY "Database" should require specific data about software (Platform, DB, etc)
CATEGORY "Mobile Phone" should require specific data about the phone (vendor, model, provider, etc)

It can be useful to force users to input some mandatory data for a category (and not for all categories)
In addition, it can be useful to filter issues and obtain statistics.