Periodically check for ATT&CK map updates after boot

[rctgardner]

Periodically (weekly?) check in on the ATT&CK GitHub site for new framework versions.

Currently, ATT&CK maps are only downloaded at application startup when called in the activate() function. Some users may prefer to keep their editors running for long periods of time, and there is no reason to miss out on ATT&CK framework updates just due to this preference.

This should be a relatively uncommon problem, especially given how often the framework is updated, but we might as well avoid it if we can. Additionally, rather than spamming GitHub with many users checking in at the same time, we should probably randomly generate the check-in time on first install. We don't wanna get the repository flagged by some weird ML system looking for C2s.

[rctgardner]

This should be easier to do by switching to https://github.com/mitre-attack/attack-stix-data/

The collections[].versions[].version key inside index.json contains each available schema version.