Add zero values for when there are no data

[jheeffer]

When there is no data, we should add zero's. https://docs.google.com/spreadsheets/u/1/d/1EMSP8rthB6yAxj3GtPAcssfP0HHPfujRS0YDPmD1NRY/pub#

Why?

1. Then interpolation doesn't get confused (we can also mark this indicator as no interpolation, but I don't think Vizabi has that yet).
2. Bubbles will stay on the chart but at 0 when played over time (empty/null = no data so bubble is gone)

But:
Can we say no data = 0 affected/deaths? A bit iffy... especially if you go further back in time..
It seems in Gapminder World it was done starting at 1970.

I will ask Ola about this.