Account::Sync model and test fixture simplifications (#968)

* Add sync model

* Fresh fixtures for sync tests

* Sync tests overhaul

* Fix entry tests

* Complete remaining model test updates

* Update system tests

* Update demo data task

* Add system tests back to PR checks

* More simplifications, add empty family to fixtures for easier testing

test/fixtures/users.yml

@@ -1,3 +1,10 @@
+empty:
+  family: empty
+  first_name: User
+  last_name: One
+  email: user1@email.com
+  password_digest: <%= BCrypt::Password.create('password') %>
+
 family_admin:
   family: dylan_family
   first_name: Bob