Graph labels and general naming fixes

The story explains better than I do: https://www.pivotaltracker.com/story/show/55393972. Text below:

On the Tax Disc and SORN volumetric graphs
- remove 'submissions' from "Applications submissions per week over the last 9 weeks
- on hover label it should say SORN not sorn
- on hover label is should say Tax disc not tax-disc
- in services list it should be Tax disc not Tax Disc