Matthias Kuhn fdd00870ee [FEATURE] Search widget for relations using aggregates
For each child relations, the subform is visible.

Each attribute of the children has a tool button option to define to which
aggregate the specified value should be compared. This allows for searching
things like

 * Each city where the highest building is more than 300 m
 * Each sensor where the median value is lower than 50 ppm
 * Each feature with a child with a missing value
 * ...
2017-11-20 20:31:38 +01:00
..
2017-05-15 07:34:14 +10:00