Merge branch 'feature/use-guzzle' into 'master'

classes/UrlHelper.php

composer.json

composer.lock

js/CommonDialogs.js

tests/UrlHelperTest.php

vendor/composer/installed.json

vendor/composer/installed.php

vendor/guzzlehttp/guzzle/CHANGELOG.md

vendor/guzzlehttp/guzzle/README.md

vendor/guzzlehttp/guzzle/UPGRADING.md

vendor/guzzlehttp/guzzle/composer.json

vendor/guzzlehttp/guzzle/src/Cookie/CookieJar.php

vendor/guzzlehttp/guzzle/src/Cookie/SetCookie.php

vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php

vendor/guzzlehttp/guzzle/src/RequestOptions.php

vendor/guzzlehttp/guzzle/src/Utils.php