fix directory separators for WinRT

internally we always use forward slashes

Change-Id: I0573d63b993bb76bc5798ee060fe9bdfb7304658
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
WinRT: implement QStandardPaths

need to leave some items out like media folder access, as this is not
available by default and also requires certain capabilities to use
those.

Furthermore updated the tests for sandboxing as well as skip cmd.exe
related tests as that does not exist on WinRT.

Change-Id: I992b1e195b79615bea0be4f84f56cfb8f0d902bf
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>