[1455] First attempt at year segmentation
Style using right and down chevrons as requested
Handle date parsing a bit better

To handle case where someone enters MM/YYYY. The form says that they should us
DD/MM/YYYY but it isn't enforced.
Improve date parsing
Move JavaScript into .js file
Merge pull request #21 from datagovuk/1455-year-segmentation

1455 year segmentation