Tracking failed downloads in analytics.
Remove downloadfailed analytics, move download logic to MirrorStore, and
set up secure mirror logic.
Force revalidate download key if user or access token changes.
Make ping URLs use the new secure mirror system.
Replace "processing version" with info about what library we're looking at
No validation anymore
Re-introduce validation.
Make the validation request work in this brave new post-refresh world.
Remove validation logic.
Add url rewriting to secure mirror, reactivate validation.
Validation comes back out.
Merge pull request #4 from TechnicPack/master

Huge update