Added Flickr client

Based on the Twitter client. Added the param oauth-callback to
oauth-request-token, otherwise flickr complains with
"oauth_parameters_absent=oauth_callback". Added the params
oauth-consumer-secret and oauth-token-secret to oauth-access-token
otherwise flickr complains with "oauth_problem=signature_invalid".
Merge pull request #10 from tobiasjewson/master

Added Flickr client