Make "Load Resources from Wayback Machine" checkbox sticky

[Mr0grog]

The “Load Resources from Wayback Machine” checkbox has done a pretty good job of making our pages render more accurately, but it can also slow page loads down significantly for pages and sites that aren’t commonly in the Wayback Machine’s cache. That can really slow down some analysts’ work.

To alleviate that, we’d like to try making the value of the checkbox “sticky” — it should keep its value across page loads and views. This is probably best done using the same kind of layered session/local storage mechanism described in #192.