allow tests against ajax requests

this helps tieing together the "normal" menus and the MobileMenu and
makes them both implement a getItems() method.

SVG based page tools

* 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
  ...

this ensures installed composer libraries will be compatible even when
installed from a higher version platform

This doesn't really do much except wrapping the functions into a
namespaced class. Autoloading takes care of loading the file.
It's now possible to call lib/exe/ajax.php multiple times in a test
request.

* origin/pr/2054:
  cleaning
  extracted functions added test coverage
  allow tests against ajax requests

Translation update (sr)

Translation update (sr)

Translation update (sr)

Translation update (sr)

Translation update (sr)

This should reduce the complexity of the function

Fix more PHP Notices

This fixes the PHP Notice when $headers['Content-Type'] is unset. It
also allows for easier extension later, e.g. adding handling for a JSON
content-type.

If a key is not set, a PHP Notice is triggered. While these are
currently suppressed, this is still a code smell.

This function might be called by an plugin with an array that has only
string keys and hence no key 0. This would trigger an PHP Notice when
trying to get the first key's level.

If an config value is not set in the input lines, initialize it as empty
string to prevent PHP Notices complaining about $line[1] being not set.

A PHP Notice occurred when $url didn't contain a '?'.

Prevent duplicate "selected" attributes in option tag in Form.php (DropdownElement)

Corrected external link syntax, now requires preceding whitespace.

hopefully this will help with figuring out why our HTTP tests sometimes
fail on travis.

Update check supports HTTPS (without fallback)

If SSL is not supported, a HTTP request will be made. In the log the request type will be indicated, but on the frontend no additional message would be shown (I think it's better to notify admins about non-SSL situations, but currently when this fetch encounter error, no error message will be shown, so it's better not to add any warning).