Feature: Custom field grouping (low hanging fruit)

[svoop]

With #656 (almost) out of the way, there might be an easy to impement solution for grouping custom fields. Here's an example:

Given an (ordered) list of custom fields:

The items without value could be considered group titles and therefore rendered differently in the view. This way, no changes are necessary on the underlying kdbx structure, but the 1Password importer can take a leap forward and maintain ordering and grouping with group titles of custom fields.

Also, the behavior complies with the principle of least surprise: Custom fields without a value are not rendered (since they don't carry a payload) unless when sorting is custom.

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With "sort: custom", these group titles are rendered upcased+bold and the function icons are omitted:

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With "sort: ascending", the group titles are not rendered at all.

[strongbox-mark]

That is an interesting idea, I don't hate it... It would be a non standard extension though so I'm always a little dubious, I don't want to place work on devs of other KeePass compatible apps. Worth considering though... Thanks.

[svoop]

Since it doesn't break anything existing, maybe worth asking upstream whether it could make the specs for kdbx. This under the assumption that ordered custom items are part of these very specs and not an addition of Strongbox which isn't stored in the kdbx itself.