Registration of anonymous patients

There are times when it's necessary to register a patient where that patient's name is unknown at the time of registration. In order to accommodate this the following changes should be made to the registration app:

• Similar to the toggle for whether the date of birth is known, we should have a Yes / No toggle for whether the name is known.
• If the name is known (default), things proceed as they do today
• If the name is not known, the name fields should be hidden and when the patient is submitted the following things should be done:

1. The first name is set to a configurable value, defaulting to "UNKNOWN"
2. The last name is set to a configurable value, defaulting to "UNKNOWN"
3. The person attribute "Unknown patient" should be set to "true"

If at a later date, the patient's name becomes known, the user should be able to turn the toggle to "Yes" and then fill in the patient's name. At that point the "Unknown patient" attribute should be set to "false".