Visualization Query Builder: aggregate and field selection

[aaronleopold]

Describe the bug
Choosing a field before aggregate, then choosing aggregate overwrites the entire aggregate with field.

To Reproduce
BAR CHART CONFIG FORM:
select genus for field 1
select aggregate COUNT for field 2
select specificEpithet for field 2

--> you'll see SELECT genus, specificEpithet ...
--> expected: SELECT genus, COUNT(specificEpithet) ...