Reuse flickrapi's cached token

[olberger]

AFAIU, there's no need to replay the auth scenario every time, as flickrapi caches (in ~/.flickr/) the tokens.

See my proposed change in : 24a1a65 to do so.

[jmathai]

I didn't know that was cached. Looks good to me. Send a PR :)

[olberger]

https://github.com/openphoto/export-flickr/pull/11 ;-)