Fix flickr helper external_url and caption
Make api calls multi-threaded
Skip foursquare venues when there are no photos
Redo twitter helper to only send back tweets that are properly geocoded and have attached photos
A couple more fixes for the flickr helper
Made it so that foursquare helper returns two most recent images from each trending venue
Merge pull request #17 from ahegyi/flickr_fixes

Fix/update/tweak flickr, foursquare, twitter helpers & make API calls multithreaded