Added EBS to AWS Calculator

I was unsure if i'd be able to add any new features during the week since I tend to be swamped with work from my full-time job.

However, today ended relatively quietly at work so I figured I could try to crank out something before the day is done. EBS was the next most obvious feature as both EC2 and RDS uses it. It's not yet perfect but I'm glad I got something out.