add contact form and mailing

Co-authored-by: Constantin Simonis <constantin@simonis.lol>
Reviewed-on: http://git.simonis.lol/sites/abiball/pulls/6
Reviewed-by: Constantin Simonis <constantin@simonis.lol>
Co-authored-by: Jan-Marlon Leibl <jleibl@proton.me>
Co-committed-by: Jan-Marlon Leibl <jleibl@proton.me>

.env

@@ -18,3 +18,8 @@
 APP_ENV=dev
 APP_SECRET=
 ###< symfony/framework-bundle ###
+
+###> symfony/mailer ###
+MAILER_DSN=smtp://${MAILER_USER:-null}:${MAILER_PASSWORD:-null}@${MAILER_HOST:-localhost}:${MAILER_PORT:-1025}
+CONTACT_MAIL=${CONTACT_MAIL:-contact@localhost}
+###< symfony/mailer ###