frontend & backend changes to vote: use the verb "Like" and "Dislike"

## Changes
- Rename "up", "down" vote to "Like" and "Dislike".
- Update css to use thumbs icon
- Give it a tooltip text
- Hide "Bookmark" button


### Before
![Screen Shot 2013-01-31 at 9 54 35](https://f.cloud.github.com/assets/184520/113165/f25a5a1e-6b40-11e2-8ac2-c933684cc655.png)

### After
![Screen Shot 2013-01-31 at 9 55 21](https://f.cloud.github.com/assets/184520/113164/ef0ade88-6b40-11e2-97ae-4bfb36d30669.png)