Custom EA loading into map feature

[BasDekker-Zenmo]

Possibility for user to load solarfarms, windfarms, and grid batteries with adaptable settings into the model.

Phase 1 of the pull-request:

• Feedback on the fundamental/structural implementation and location of the code and shapegroups
• UX
• Debugging

Afterwards, phase 2 with focus on appearance of UI

Merge with zero_engine pull request: Zenmo/zero_engine#287

[Luc-Sol]

General remarks:

• Do we have a better name for these GCs? I don't like calling them EAs and we already have 2 types of sliderGCs. (General & EHub)

UX:

• How do you select the top GridNode T0? You can't this feature is to create GCs that you want to connect to a specific GN,

• Adding new GCs does not update the legend if it is the first of its kind.

• The button 'remove all' only refers to these custom GCs, could it be confused by users to refer also to the sliderGCs above?
  Should there be a clearer distinction between the two sides of the tab?

UI:

• The objects get some polygon on the map. Are we going to scale those with the size of the assets?

CODE:

• What is the point of 'b_removeAllCustomEAs' ?

• The functions to add the different types of custom GCs are very similar. The overlapping code should be seperated into smaller functions

• What does 'f_deselectPreviousSelect' at the end of 'f_removeCustomEA' do ? This causes the profile charts in the resultsUI to freeze. Is there a reason for adding this call or can it simply be removed?
  EDIT: This only seems to happen with multiple GCs in a single building (appartementen)

• The comment "Allow slider to affect it" in de f_addCustom... is confusing. This boolean makes sure the installed capacities are added to the total in the sliders, but these GCs will not be effected by the sliders.

• These custom GCs all have their own owner. While the 'normal' and 'ehub' sliderGCs share an owner. Why was it chosen that these create/remove new owners instead of using the existing ones?

[BasDekker-Zenmo]

• Renaming EA to GC: customEA -> customGC
• SliderGCs only add at GridNode T0
• Update legend after adding customGC
• Scale polygon based on installed capacity + make square polygon (in the future: user draws the polygon)
• Clearer distinction between sliders and buttons (or more explanation)
• Remove b_removeAllCustomEAs (unused+unneccesary)
• Separate overlapping code into smaller functions (f_addCustomGC...)
• Remove 'f_deselectPreviousSelect' at the end of 'f_removeCustomEA' do ? This causes the profile charts in the resultsUI to freeze. Is there a reason for adding this call or can it simply be removed? EDIT: This only seems to happen with multiple GCs in a single building (appartementen)
• Adjust comment "Allow slider to affect it" in de f_addCustom...
• Use existing sliderGC owner. Do not create + delete owner