Upvote and downvote solutions

Upvoting and downvoting solutions should now be up and running.
There are a few issues with this but we can address them in a later merge.
1) It's slow. Currently it waits for the network call to finish before it updates the UI.
2) Whether or not a user has voted on a solution does not appear to be persistent. Voting on a solution, then restarting the app (via reinstalling or by turning the phone off and on) allows you to vote on that same solution again.