ypes, callback)
		 * type: either "drive", "dropbox", or "onedrive"
		 * fileTypes: array of file extensions (including dot before) (leave empty to allow all) [ignored on dropbox :(]
		 * callback: function to call when either the file is ready, or the user cancelled it
		 * 
		 * this object is passed to the callback function:
		 * message: either "success", "cancelled", or "error"
		 * if success, name: name of the file
		 * if success, data: file contents (arrayBuffer)
		 */
		
		var fileTypes = [".docx"