Added icon for billing.

Currently, it jsut sends you to google.
Make billing thing actually do something useful.

Note that I don't really have a good way of exactly testing all
the datastore stuff, but it should work.
I am a little unhappy with the code duplication that was required
to implement this. I'll work on that.
Merge pull request #9 from djpetti/new_payment

Added Billing Info Option to Dashboard