Implement logical unique constraints on Magician

[marknelsonengineer]

There should be a few 'rules' preventing duplicate Magicians:

• firstName + " " + lastName
• email
• stageName

The rules should be validated in EditMagicianFormData.validate() with helpful messages such as: The Stage Name 'Slydini' has already been taken.

[pkarjala]

We can use the @Unique constraint to help with the DB implementation.

[pkarjala]

This will be email only at this time, as we do not want to prevent people with the same name from creating an account. We also do not require stageName at account creation, so we will need to migrate that to make it a required field in order to consider making it a unique constraint.

[marknelsonengineer]

Done