move mobile phone to optionals - require for speakers when reg. talk

[oma]

Asking for phone number seems invasive. We require it for speakers (last minute panic call when they show up late).

Taks:

1. Move "Telefon" from registration form to "optionals" See issue Optional user/participant registration details #8
2. Ask mobile number from speaker (if missing) when he registers a talk.

[karianne]

Just want to add that phone number was also used to reach users that signed up, but never paid and didn't reply to emails.

[oma]

how did that turn out? wrong email?

[karianne]

That has happened too, but mostly it's people that for some reason apparently are physically unable to reply to an email. Or three. "Oh, I was supposed to fix that..."