[geary] (23 commits) ...Merge branch 'mjog/493-undo-send' into 'mainline'

[Michael Gratton <mjog src gnome org>]

Summary of changes:

  e426517... Rename Config class and source file to match code style (*)
  455eb77... Let Application.Command instances specify if they support r (*)
  9b4edf5... Util.Email.to_short_recipient_display: Consider all of to/c (*)
  cc4389f... Make Geary.ComposedEmail implement Geary.EmailHeaderSet (*)
  4380323... Replace Geary.Account::send_email w/ Smtp.ClientService met (*)
  1447d1a... Minimise DOM changes made by ComposerPageState::cleanConten (*)
  29042bb... Move composer classes into their own namespace (*)
  44fd565... Clean up the Composer API (*)
  97e9299... Clean up Composer.Widget header management (*)
  0128d76... Clean up how Composer.Widget's presentation mode is updated (*)
  bc78622... Rework Composer.Widget close management (*)
  884d48b... Minor Application.Controller shutdown cleanup (*)
  8f85397... Add undo-send-delay application setting (*)
  ce40974... Implement undo-on-send (*)
  df50fb0... Update composer draft lifecycle management (*)
  19e0424... Make Application.Controller's composer command re-usable (*)
  3735040... Implement undoing discarded composers (*)
  de57355... Implement undoing saved composers (*)
  c5c36ee... Don't prompt when closing in-main-window composers (*)
  e4a02ee... Ensure saved drafts are reused when reusing Composer.Widget (*)
  f7ea988... Remove unused method (*)
  07f6f02... Clean up composer handling on application quit (*)
  2ed60bf... Merge branch 'mjog/493-undo-send' into 'mainline'

(*) This commit already existed in another branch; no separate mail sent