New sidebar

Restyled the sidebar so it's clearer to understand what step you're on. 

Added in:
* checkmarks for complete steps
* right arrow for current step
* empty circles for future steps
If you like, but this is assuming that the active link and body text color are related + the same. Like if we wanted the active link green, then all body text would be green. I can see potential for making these a different color.