Auto refresh token

[gdmalet]

I have the misfortune to own a Suunto watch, and recent horrific changes to their website / app made me need to drop Suunto and move to Strava. Unfortunately that involves uploading around 2000 activities, which with Strava's rate limits is going to take a few weeks. To this end I wanted to put the uploads into a daily cron job, and just leave it to do its thing. To do that, I needed to fully automate dealing with the OAuth tokens, which I have now done.

The changes in this pull request result in the details gathered by strava_local_client.py being stored in a file, which from then on is read by, and updated by, uploader.py. It just needs to be run once a day, and it will continue uploading where it left off.

I'm not sure this is something you want? Changes are in a few commits, but each is simple. I could merge them into one commit if that helps. Total code changes are pretty small though.

Thanks, and thanks for writing strava-uploader - it has been really useful to me! g