Use html5 validators on forms fields

We have an old system of validation that doesn't check every cases (emails with @ in it, etc), and we have scripts for things that are native in recent browsers.

We should use:

• required attribute on inputs
• new input types (search, email, url, tel, number, range, date, month, week, time, datetime, datetime-local, color)

... to not annoy people that have recent browsers, and avoid people using Studio to write their own validators without providing the standard basis.