Fixed #267 Email verification feature (#268)

* <Implemented basic welcome email upon signup>

* <Added config option to enable>

* <Added verification link routing>

* <Added views for verify/resend and reconfigured routes>

* <Finished Verification System minus Rspec changes>

* <Fixed code style>

* <Modified dome rspec tests>

* <Switched sample env back to default>

* <Added test cases to increase code coverage>

* <Added test_helper>

* <Minor code changes>

* <Added requested changes>

* <Added requested changes>

* <see if this fixes migration>

* <see if this fixes migration>

* <fixed migrations>

* Delete .rake_tasks~

* Update _confirm_button.html.erb

* Update _resend_button.html.erb

* Update verify_email.html.erb

* Update verify_email.text.erb

* <Fixed bugs>

* <Added validation of verification link and fixed some code style>

* <Disabled updating email for omniauth>

test/mailers/previews/user_mailer_preview.rb

@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class UserMailerPreview < ActionMailer::Preview
+end

test/mailers/user_mailer_test.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class UserMailerTest < ActionMailer::TestCase
+end