[geary] (10 commits) ...Merge branch 'mjog/rfc822-cleanup-part-n' into 'mainline'

[Michael Gratton <mjog src gnome org>]

Summary of changes:

  b78dfe7... Composer.Widget: Convert references to a MessageIdList inst (*)
  537410f... Geary.RFC822.{MessageID,MessageIdList}: Throw error parsing (*)
  26f5fde... Geary.RFC822.Message: Suppress message id errors in ctors (*)
  0b8bf73... Geary.Imap.EnvelopeDecoder: Suppress message id errors (*)
  e2f2b6c... Geary.RFC822.Message: Add accessors for message headers and (*)
  6af5b2f... Geary.Email: Rework RFC822.Message.get_email into an Email  (*)
  784bac5... Geary.Imap.FolderSession: Tighten up preview generation err (*)
  c2a1bae... Geary.Memory.OffsetBuffer: Remove now unused class (*)
  53ddf81... Geary.Imap.FolderSession: Ensure Email fields updated for n (*)
  e89a5ca... Merge branch 'mjog/rfc822-cleanup-part-n' into 'mainline'

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