Refactor EPP users to API users

app/models/api_user.rb

@@ -0,0 +1,24 @@
+# rubocop: disable Metrics/ClassLength
+class ApiUser < ActiveRecord::Base
+  # TODO: should have max request limit per day
+  belongs_to :registrar
+  has_many :contacts
+
+  validates :username, :password, :registrar, presence: true
+  validates :username, uniqueness: true
+
+  attr_accessor :registrar_typeahead
+
+  def registrar_typeahead
+    @registrar_typeahead || registrar || nil
+  end
+
+  def to_s
+    username
+  end
+
+  def queued_messages
+    registrar.messages.queued
+  end
+end
+# rubocop: enable Metrics/ClassLength