Feature/add more hooks

The plugin is now able to

1) Register users & page views using the 'image' action hook which hopefully prevents php blocking when determining if users exist and what items they have looked at

2) Register ajax calls for when actions like 'likes' and 'dislikes' are executed via events like the clicking of buttons

3) Registered actions for adding items when new items have been saved in the back end

Also wrapped a lot of the calling functionality in try catch blocks to handle different scenarios like 404 or when the prediction server is offline

Added user settings for the recommendation and similarity engines in the plugin settings page