Store Logos Releases in a Cache File

[thw26]

I'm thinking in .local/state or somewhere similar. Ideally if we do this, anytime an update is run, we would compare the cache file to what is on the web, and either append the new or replace the whole. We could probably reduce the rate at which releases are checked for to once a week unless a force flag is passed.

[thw26]

We could do something similar with GitHub data and the md5sums to reduce GitHub API calls.