Feature grid connection child agents (#109)

* Child agents for gridConnections

*GridConnections are succesfully instantiated as child agent types for:
-Houses
-Buildings
-Districtheating
-Solarfarms
-Windfarms
*GridConnections override f_operateAssets() function with their own (e.g. f_operateAssetsHouse() ) function. Still empty, operation code not ported yet!

* EVs to households and operating asets

- evs now only in households
- connect to parent agent for household now also overwritten
- minor startup code fixes to fit current architecture
- each GC type now operates

Co-authored-by: JorritvandenHouten <[email protected]>