Strava tools

[MigoMueller]

Add interface with Strava: download recent rides into a user-specified directory, provide wrapper for uploading rides.
I've messed with this before, but stravalib has since been upgraded to 0.6 with changed user authentication (OAuth2).

[MigoMueller]

Got the authentication to work (in an .ipynb; to be adapted to importable scripts).
Problem: Strava API does not offer straightforward download capability (although the web interface does, even with /export_original...
Need to figure out what to do about this.

[MigoMueller]

Authentication part has been solved (issue #9). Now make stravaUploader more versatile. Maybe break authentication into separate class?

[MigoMueller]

Authentication and upload done (issue #11). Class stravaAtHome now sub-classes stravalib.Client.
Next thing to do: support activity download as GPX (issue #14).