Merge branch '4.4'

* 4.4:
  Fix a few minor misprints in Mailer article
  deprecating Swift Mailer and moving all docs into one spot and moving many docs from mime to Mailer and writing it
  Yet another great review!
  Add link to usefull online editor
  Fixes after thorough reviews!
  Removed further usage of transchoice in the docs
  Added documentation on the ICU MessageFormat
  Some general fixes/improvements for translation guide

Author: wouterj

_build/redirection_map

@@ -417,3 +417,6 @@
 /workflow/state-machines /workflow/introduction
 /workflow/usage /workflow
 /introduction/from_flat_php_to_symfony2 /introduction/from_flat_php_to_symfony
+/email/dev_environment /mailer
+/email/spool /mailer
+/email/testing /mailer