Organization: add null constraints and update org create service

[kasugaijin]

Please add null constraints on organizations table in the database for name, slug, email and then update then add email attribute to the Organizations::CreateService when creating an Organization.

Also on the Organization model, we need to validate: name for presence slug for presence and also do not allow any characters that are forbidden in URLs. Look into options for validating this slug. email for format, presence.