Changed header to 'contact us' for clarity

Need to make it clear to users that they can expect us to reply - rather than just send in their feedback.
Merge pull request #25 from ministryofjustice/Leigh_updates1908

Changed header to 'contact us' for clarity
Add specs for visit helper
Lead days to exclude current day
WIP exclude weekends
Added a Schedule object to wrap permissible dates and the logic behind them.
Removed unused methods from VisitHelper.
Added a test for prisons that work on weekends.
Assume that no prisons work on the weekends.
Some prisons work on weekends.