updated header to only show not me on auth page
using rails helper instead of string
resolving dependency on request object
Implement requested changes from #191

Account --> Your Profile
This is not me --> functional sign out link

There's an issue where "This is not me" should allow switching
of accounts.  Will file an issue for that.
Merge pull request #233 from 18F/feature/not-me

Only show This is Not me on the oauth authorize page