Updated pannellum submodule to 2.0.1 tag
Work with older php version

Do not require a php version which allows to directly resolve array
entries after function calls.
Try to support SSL correctly

* Use https:// url to pannellum, if ssl is used for the request
* Try to use relative paths to the config file etc so that SSL is chosen
  automatically if used. I am pretty sure that this will not work for
  all wordpress setups, but generally it seems that there is no decent
  support for plugin authors to correctly construct URLs to resources.