Email change to existing email

[UnspeakableHorror]

Fixes https://github.com/natebenson/vyllage/issues/1110. Fixes https://github.com/natebenson/vyllage/issues/1111.

• Added a new test user: vytst@mailinator.com.
• Fixed some Codacy errors and warnings.
• Changed validation to take into account if an email already exists and return an error.

[tylerbenson]

Assigned to @kalobkalob for validation.