Should we save assets locally to avoid request loading from server every time?

[chaosprint]

When calling asset::url
check if ~/Document/Ambient/GAME_NAME/content/assets/ASSET.FILE exist
if not, request it from the server

In future web version, we can use Web Storage API

related to this PR: #290

[philpax]

Yes, we had this originally; we ended up disabling it because it would use the old versions of files instead of new files. The solution to this will probably involve #12.

[FredrikNoren]

Like @philpax said, this already exists, but we need to implement cache invalidation: #81 Closing this issue in favour of that one.