Handle multi value fields

[splitbrain]

I'm not sure what to do with them. For label and title I would just use the first value. But dates are tricky. I see two options:

• allow the use of only one date field if it's a multi, use the (ordered) dates from it in pairs and create multiple tasks in one lane
• require that both date fields are multi, use pairs from first/second to create multiple tasks in one lane

What would happen with overlapping dates?