Contact model changes (#184)

* move source id from contacts

* Fix contactInbox model name

* rubocop fix

* Fix rspec

spec/models/contact_spec.rb

@@ -5,12 +5,10 @@ require 'rails_helper'
 RSpec.describe Contact do
   context 'validations' do
     it { is_expected.to validate_presence_of(:account_id) }
-    it { is_expected.to validate_presence_of(:inbox_id) }
   end
 
   context 'associations' do
     it { is_expected.to belong_to(:account) }
-    it { is_expected.to belong_to(:inbox) }
     it { is_expected.to have_many(:conversations).dependent(:destroy) }
   end