Remove duplicate lowercase QpxeExpress.php
Merge pull request #136 from tagged/remove-dupe-qpx-class

Remove duplicate lowercase QpxeExpress.php
Use refresh token when revoking access if available

Previously we would only ever use the access token, which may have expired.
Now, use the refresh token preferentially if present.
Use single quotes on $ sign

Avoids potential issue on older PHP. Fixed #128
Fixing collection to use new private modelData
Merge pull request #138 from ianbarber/master

Fixing token revoking and change URI template quoting