Multiple speaker links for joint sessions

[chris48s]

Currently we only have the ability to attach one link to a speaker.
Sometimes a session is presented by two people so they either have to have no link or a link to their project. It would be nice if we could specify an individual link for each speaker (using the existing CSV-based workflow).

[chris48s]

Looking over the sites for the last few years every talk has had either one speaker or two. We don't really need to support N speakers.

Probably the simplest solution to keep everything editable via CSV/google sheets would be to make the structure something like

name1	name2	twitter1	twitter2
David Selassie Opoku		sdopoku
Monica Granados	Lily Zhao	monsauce	lily_z_zhao

Then do something like

{% if speaker.twitter1 %}
  <a href="https://twitter.com/{{speaker.twitter1}}">{{ speaker.name1 }}</a>
{% else %}
  {{ speaker.name1 }}
{% endif %}
{% if speaker.name2 %}
  {% if speaker.twitter2 %}
    and <a href="https://twitter.com/{{speaker.twitter2}}">{{ speaker.name2 }}</a>
  {% else %}
    and {{ speaker.name2 }}
  {% endif %}
{% endif %}

in the template (i.e: the second speaker is optional but displayed if present).