Merge branch 'master' into svgpagetools

* master: (72 commits)
  fix platform to the minimum requirement
  translation update
  translation update
  translation update
  translation update
  translation update
  replace conditional with array_pad
  refactor: more extensible Content-Type header handling
  fix: correctly show conflicts in extension manager
  fix: check if key is set to fix PHP Notice
  fix: access first element of associative arrays
  fix: set default value for empty var
  fix: initialize vars to prevent PHP Notice
  adjust default bcrypt iterations to 10. fixes #2093
  always send Vary: Cookie header. fixes #1594
  moved function and fixed whitespace errors
  show more info on failed HTTP requests
  do not export the appveyor config
  Added appveyor config for automated windows testing
  Update check supports HTTPS
  ...