Added labels on attendee fields form to improve accessibility #a11y

[willybahuaud]

Hello,

When I use Camptix, I'm a little frustrated that a click on a field description doesn't focus the field. So I suggest to add a label around fields description (on the attendees form), targeting concerned inputs.

[iandunn]

This looks good at first glance. It'd be a good thing to review in the next bug scrub (probably post-GDPR).

[GaryJones]

Has some merge conflicts which would need to be resolved.