Implement persistant cache

[software-opal]

Implement a cache that persists across page loads. Currently the browser caches most requests, however if we were able to have a persistent cache we could implement more aggressive caching such as the kinds described on this issue

[glasnt]

For now, I think having it browser side is fine. Add a bit of polish on the loading mechanics, and it doesn't appear to be too annoying in it's current speed, even with reloading.

IIRC adding any caching outside of the browser will require a physical presence, which is fine, but it's more moving parts and maintenance.

I'm more than happy to leave it as is for now. 😄