- Make position props on buttons optional
- Move UIElement creation back to Factory instead of within Section

Use a horizontal aligned placeholder for dynamic aligned drop lists
when there is more than one element in the list

- Refactor variable of the placeholder dimensions

- Important for vertically positioned drop lists
- Analogous to the calculation of the height

- Replace pixel calculation with percentage values
- Use of only two modes: full fill or line

#291

#343

#294

Red background looks really bad, so we just adjust the border color.

- remove ID handling from model classes. This is now done by the editor 
itself (mainly unit service).
- Rename and move IDManager to editor as IDService

Just called from the editor, before creating the Unit instance.
It goes through all IDs and checks for duplicates. If found it generates 
a new one and shows the prompt.

Transform string array to Textlabel array.

#338

i.e. something has been clicked.
Since the value is not used on the player, we also need to check the 
FormControl value.

#335

had some issues with the switch to the new options stuff.

When calling the element constructor may generate IDs. Those appear as 
already registed later when the unit is instantiated for real.

- Do ID checks only in the class, not in unit service (or elsewhere)
- Fix repaired value list to get new objects instead of references to 
the existing.

There should never be the case, therefore error out.

Use map and flat instead of reduce to set dragNDropValueObjects