migrate learnings around typescipt DisplayItemModels and sub-interfaces about songhaycore

[BryanWilhite]

the main ‘learnings’:

• the addition of selectable
• the Map<string | number, any> in selectable [src]
• the addition of groupable [src]
• addition of temporal properties to DisplayItemModel: end/incept/modification dates

the Tag and ItemCategory properties have to be removed from ISortable [src] because of the map in selectable and the addition of groupable, respectively

the category concept (probably borrowed from my exposure to OPML) is being replaced by the group concept which is kind of a breaking change 🔥; the word category was originally used to associate a type with a Display Item—group names based on types can do the same thing

the historical need to categorize on the DisplayItemModel can regarded as a suggestion to use the MenuDisplayItemModel instead

this implies that DisplayItemModelCategories [src and src] is misnamed and breaking changes need to be made in DisplayItemModelExtensions [src]

[BryanWilhite]

removal of DisplayItemModelExtensions.Has*Category methods and DisplayItemModelExtensions.WithItemCategory will break a lot of GenericWeb code 🔥

equivalents of these members will be replaced by MenuDisplayItemModelExtensions.HasGroupId (and DisplayItemModelExtensions.HasTag) because, again, categories are moving to groupings

finally DisplayItemModelCategories will be renamed to MenuDisplayItemModelGroups