NCI-Agency/anet#2926: Add vertical layout option to CustomFields
NCI-Agency/anet#2926: Add vertical layout option to CustomFields

This makes it possible to display groups of custom fields in a
vertical layout, with the label above the input field.

Note that this doesn't work yet for DateField, EnumField and
EnumSetField as the components used to render them need some
styling changes in order for this to work.

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