Remove hint bounding for copy

This is no longer needed and is broken when using lists with markdown anyway.
Further copy changes to maternity-paternity-calculator

Addition of hint text and updated wording.
Fix bad grammar
Merge pull request #191 from alphagov/maternity-paternity-copy-updates

Maternity paternity copy updates
Merge commit '92a215fb7b3898a149d0c2e5acfb6f0b2c55dcf2' into HEAD