Gracefully handle lack of localStorage

[jbodner09]

The Third-Party cookie blocking setting in browsers ends up blocking all forms of storage, not just cookies:

I suspect turning off all cookies would also do the same thing. When this happens, PuzzleJS hits an error during startup when trying to load previous state, which ends up preventing the entire puzzle from loading:

It should be easy to detect when localStorage is available via a try-catch block, and when it's not, alert the user that state won't be saved.