Clear local storage data upon new version of AS

#### To test:
 - npm install
 - grunt build
 - Run your web app with recently compiled version of AS and make sure that local storage has new  AS_version key that matches with its compiled version from package.json. 
We shouldn't be using localStorage.clear since we might be erasing data we don't handle.  
Notice that every key saved in localStorage by activitystream starts with "AS/". You should iterate the localStorage and delete only those.