Fix icons and typos in ui tour

Fixes #6639 , or tries to. The x icon is too large still, and the forward/backward buttons aren't aligned correctly:

![image](https://cloud.githubusercontent.com/assets/83444/4538577/18bfc12c-4df2-11e4-837e-b9483e3ab488.png)

I imagine this should be something pretty easy to fix with the right CSS classes, but my knowledge of CSS is lacking.