[geary/wip/713150-conversations] (14 commits) ...Merge branch 'master' into wip/713150-conversations

[Jim Nelson <jnelson src gnome org>]

Summary of changes:

  d62ef74... Updated Kazakh translation (*)
  6b0e57a... Updated Slovak translation (*)
  a0af6a8... Finnish translation update (*)
  21d66b0... Updated Slovak translation (*)
  f33b0bd... Split main toolbar into two halves (*)
  32cd33a... Use composer headerbar for main window when composing new m (*)
  1fec04a... Set title of composer headerbar segment from subject (*)
  36f3168... Provide custom close-and-save and close-and-discard buttons (*)
  5162914... Move search entry out of header bar and into dedicated sear (*)
  2f7b486... Set close button on proper side of main header bar (*)
  7007c36... Move empty menu and titles to left header, ensure app menu  (*)
  fca3225... Put conversation subject in conversation header (*)
  ef87b0d... Display participants in subtitle of conversation header (*)
  3231f40... Merge branch 'master' into wip/713150-conversations

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