Don't allow creation of mix profiles

1. Create a profile. eg "My test Profile"
2. Add Individual field "first_name:.
3. Now when you go to add another field. We should ONLY allow adding of fields of Type "Individual" and "Contact"

From: CRM-3601
Example: Create a Profile and put a single field in it - Contact >> Nick Name
Profile Used For = User Registration

NOTE: If you edit the Nick Name field - and change it to Last Name (for example) - then the Profile Type is switched from "Contact" to "Contact,Individual" (which works in User Reg). If you then edit the profile field again and change it back to "Nick Name" - the Profile Type is STILL "Contact, Individual".

I guess whenever you add/edit or delete profile field we should recalculate profile type.