Soft logout

At present, stripes-core's logout facility works by loading a new page at /, causing a slow reload. If the `softLogout` option is selected, then instead it simply discards certain information about the session, which is instantaneous.

But the soft logout does not clear the Redux store – which is why nielserik prefers the hard one. I want to extend the soft logout to clear the Redux store, then make it the default.

(Very fast logout is important to me, as I constantly switch users as I test the extensive permissions work.)