Date component uses label rather than fieldset with legend

[edwardhorsford]

The date component uses fieldset with legend, and then hints and errors get associated with the fieldset.

At the moment this component outputs a label, not a fieldset and legend. Hints get linked to a wrapping div rather than the fieldset.

[colinrotherham]

Thanks @edwardhorsford, I've fixed this in #267

I've replied in #214 (comment) showing the change to label legend