Fixes #1239

Created by: davemevans

This allows stream types other than video and audio to have settings saved in and retrieved from local storage.

I've added a method to translate the old keys to new ones, but it might be that we chose to say that over the 2.0 -> 2.1 version transition the history is lost, in which case translateLegacyKeys and associated stuff could be removed.

Added try {} catch around instances of localStorage.setItem since this can throw if quota is exceeded.

Also added a test for availability of window to simplify testing of RepresentationController which indirectly depends on DOMStorage.