Cache improvements

So we really should create our own cache table on install, our cache items are fairly long lived.

Also, maybe we should ship with some pre-hashed arrays of data for the more popular projects. This would allow people to get a quick lowdown on the status of their install without having to download everything again. They would still have to download stuff if they wanted to do a diff, but that probably won't happen if they're not different in any case.

The shipped hashes should only be imported on install, and users should be able to clear the cache to force a local hash.