Refactor contact mailer

- Send single email with new email in `to` and old email in `bcc` fields
- Remove `Que::Mailer` (#895)
- Add preview
- DRY templates
- Add tests
- Extract translations
- Remove useless specs

app/views/mailers/contact_mailer/email_changed.html.erb

@@ -20,10 +20,7 @@ Kontaktandmed:<br>
 <br><br>
 Palun veenduge, et muudatus on korrektne ning probleemide korral pöörduge oma registripidaja poole:
 <%= render 'mailers/shared/registrar/registrar.et.html', registrar: registrar %>
-<br><br>
-Lugupidamisega<br>
-Eesti Interneti Sihtasutus
-<br><br>
+<%= render 'mailers/shared/signatures/signature.et.html' %>
 <hr>
 <br><br>
 Hi <%= contact.name %>
@@ -44,6 +41,4 @@ Contact information:<br>
 <br><br>
 In case of problems please turn to your registrar:
 <%= render 'mailers/shared/registrar/registrar.en.html', registrar: registrar %>
-<br><br>
-Best Regards,<br>
-Estonian Internet Foundation
+<%= render 'mailers/shared/signatures/signature.en.html' %>

app/views/mailers/contact_mailer/email_changed.text.erb

@@ -20,9 +20,7 @@ Kontaktandmed:
 
 Palun veenduge, et muudatus on korrektne ning probleemide korral pöörduge oma registripidaja poole:
 <%= render 'mailers/shared/registrar/registrar.et.text', registrar: registrar %>
-
-Lugupidamisega
-Eesti Interneti Sihtasutus
+<%= render 'mailers/shared/signatures/signature.et.text' %>
 
 ----------------------------------------------------------------------------------
 
@@ -44,6 +42,4 @@ Contact information:
 
 In case of problems please turn to your registrar:
 <%= render 'mailers/shared/registrar/registrar.en.text', registrar: registrar %>
-
-Best Regards,
-Estonian Internet Foundation
+<%= render 'mailers/shared/signatures/signature.en.text' %>