Tweak capitals on 'Service manager' page

- Senior Civil Servant doesn't exist as a thing
- Digital by Default Service Standard is capitalised
- Service manager is not capitalised
- Product manager is not capitalised
Remove empowerment

This word is specifically forbidden by the style guide.

https://www.gov.uk/design-principles/style-guide#writing-plain-english
Merge pull request #374 from alphagov/service-manager-tweaks

Service manager tweaks