Moved times to properties for lazy-calculation.

No need to do these immediately, for every file that may be loaded.
Updated/fix file-update call. Added atime.

Also, fixed the way that we were calling MediaFileUpload. It was throwing-off a "positional arguments" warning.

We think that we might've been setting some values to None with every update request, unless they were explicitly passed. We also think that time updates wouldn't have worked. Fixed mtime to be passed correctly, and added atime.
Implemented utimens. Wrote RFC 3339 routine.
PyPI upload.