new hustle
Finished sync conversion

May be a few bugs lurking around, but working great so far.

- all last_mod updates have been converted to
  turtl.sync.notify_local_change. bitchin.
- file downloads drastically improved, including rety delay and eventual
  giving up (in case of 3 or more failures to downlload). this should
  mitigate a lot of the idiocy when downloading files that have errors
  or dont exist.
- in general syncing appears to be working a lot cleaner now.

still need to update the Sync model to retry failed API syncs (as well
as delete successful items).