[CORE-2377] Allow optional client/contact fields to be required - Blesta

Details

Create a new page for required fields (tbd, probably under Settings > Client Groups).
A list of all optional client/contact fields should be shown. These fields are those that are set for creating a new client/contact in the UI (i.e. add a user, add a client, add a contact). It may make sense to have a multi-select option of Optional fields that you can move over to Required. Save them as client group settings.
In the appropriate models, when a client/contact is created, the required fields should be retrieved and used with the rules to require the fields be non-empty (as appropriate).

Test creating a new client, and contact, from the admin UI, as well as a new contact from the client UI and a new client/contact from the Order form.

Discovered while testing

CORE-2404 Client cannot update account or contacts when requiring Title field