Fix voting

This fixed image fetching and better messaging for when a user has no ads. I created another class for DisplayAd which abstracts away the JSON parsing, making the code a lot cleaner.

Voting now works, but the JSON response from the server comes back with everything saying: voted_on: "unavailable". This is some issue with auth thru mobile. So the button for voting always thinks it's clickable.

TODO:
- fix check for if already voted
- get nice thumbs up :+1: button from somewhere