basic WebDAV test in place now

Very first attempt to fulfill the requirements defined in #1354.

	/**
	 * we test if webDAV is working properly
	 *
	 * The basic assumption is that if the server returns 401/Not Authenticated for an unauthenticated PROPFIND
	 * the web server it self is setup properly.
	 *
	 * Why not an authenticated PROFIND and other verbs?
	 *  - We don't have the password available
	 *  - We have no idea about other auth methods implemented (e.g. OAuth with Bearer header)
	 *
	 */

@danimo @bartv2 @karlitschek @icewind1991 @tanghus THX