postTweet: withImageData: fixed plus a few cosmetic changes

- postTweet: withImageData: previously didn't use the right key for the image data (should be @"media_data[]"). Changed this so posting an image in a tweet could work properly

- postTweet: withImageData: inReplyTo: failed if an empty replyTo was supplied. Because postTweet: withImageData: called this method with an empty replyTo it would never successfully execute (always returned 400) so I removed the empty replyTo check.

- made some small cosmetic changes including adding a gitignore, removing some of the .DS_Store files, and reordering the postTweet selectors so that they appear in the same area in the file for ease of reading.