Persisting working state in localStorage

[mmmaaatttttt]

Since there's no database layer, folks don't have a convenient way of going back to old state and editing GIFs if they decide later on that they'd like to do so.

It might be nice to persist some of the GIF state information to localStorage, so that folks could come back to their graphs later for further edits. Depending on how much data we need to store, this could just be information on one GIF at a time, or potentially we could allow users to remember info on several different GIFs (favorited / saved ones, whatever the nomenclature is).