Add Fancy Buttons To Spacemacs Mode

Adds clickable and `RET`able buttons to `spacemacs-mode` that allow quick navigation to common Spacemacs things like the documentation and Gitter chat. Mostly so that new users will know how to find these important things.

![screen shot 2014-12-12 at 7 58 30 pm](https://cloud.githubusercontent.com/assets/887610/5421809/a6bd4334-8239-11e4-813d-d95406d87778.png)