add helper method to create Song and Sound from SoundCloud url
simplify API request code by using SoundCloud API, address john's comments
add uniqueness check to Sound by sound_type and location
* also add test for trying to resolve the same SoundCloud sound twice
address john's comments
* add begin/rescue
* new+save -> create
Merge pull request #19 from byronmwong/soundcloud_helper

add helper method to create Song and Sound from SoundCloud url