Feature/update confirmation email information (#145)

* Add `invited_by` foreign key to User

Allows for a User to be tied to the user who invited them

* Include `current_user` in new agent initialization parameters

* Add `shoulda-matchers` for testing associations

* Add Inviter information and associated account to welcome email

* Only show inviter info if applicable

* Update conversation spec for FFaker compatibility

Gemfile

@@ -59,11 +59,13 @@ end
 
 group :test do
   gem 'mock_redis'
+  gem 'shoulda-matchers'
 end
 
 group :development, :test do
   gem 'byebug', platform: :mri
   gem 'factory_bot_rails'
+  gem 'ffaker'
   gem 'listen'
   gem 'pry-rails'
   gem 'rspec-rails', '~> 3.8'
@@ -71,7 +73,6 @@ group :development, :test do
   gem 'seed_dump'
   gem 'spring'
   gem 'spring-watcher-listen'
-
 end
 
 gem 'attr_extras'