Add option to split 'extra' fields into sections

[milanlakhani]

This adds an optional config in settings.yml, which can put the 'extra' fields in an item's dialog box into sections to improve the appearance.

The placement of the sections config in settings.yml is as follows:

big_picture:
  main:
    sections:
      - name: Section1 name
        children:
           - Key1 name in section
           - Key2 name in section
      - name : Section2 name
        children:
          ...

This is what the item detail box looks like with and without sections: Without:

With:

CC @michaelmoss @awright @danielsilverstone-ct @GeriG966

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