Basing location of plugin assets on config constant that is already there..

__PLUGIN_ASSETS__ constant is not being used by AddPluginJavascriptFile and AddPluginCssFile. If you attempt to set this to a location outside of the qcubed directory, you will get javascript errors that the files cannot be found. But, the problem goes deeper. Also, due to a lack of documentation, users do not know how to specify a file. If you pass a file path relative to Docroot, and you are using a __SUBDIRECTORY__ settings, you will get errors because the __SUBDIRECTORY__ will appear twice in the url.