Add "percentage" unit option to "FIGUUR: Gerapporteerd aantal embryo's voor vrouwelijke wilde zwijnen per jaar"

[SanderDevisscher]

Currently we only see the absolute number of females with a given number of embryo's while a lot of stakeholders are interested in the trends in the proportion of embryo's as well. To inform about this statistic I think it would be nice to allow switching the unit of "FIGUUR: Gerapporteerd aantal embryo's voor vrouwelijke wilde zwijnen per jaar" from the absolute number into the percentage¹ of females.

¹(#females with x embryos/total number of females)*100

@jimcasaer @LynnPallemaerts @RuttenAnneleen @soriadelva any reason why not ? or any remarks ?

We just need to decide on the esthetics ?

1. stacked line (reeds gebruikt in FIGUUR: Afschot per jaar en per leeftijdscategorie (o.b.v. onderkaak))
   
2. stacked area (volledig nieuwe type grafiek)
   
3. something completely different
   

[jimcasaer]

I'm in favor of the first version !