feat: add template to flat view

[shawnyama]

Description

• Model template editing can be done in the flattened view
• As soon as a decomposed card is linked to the flattened card the same edit is applied on the decomposed side
• Any decomposed cards that are unlinked to the flattened model are ignored

How it works

• Key system behaviour (how it always worked): The flattened model updates whenever an edit is done in the decomposed view
• When I add cards/links on the flattened side it is pure UI
• Once a decomposed card is connected to the flattened card all changes translate to an equivalent edit on the decomposed side (see reflectFlattenedEditInDecomposedView)
• These decomposed edits then trigger the key system behaviour ^ which "reflattens" or "merges" what's on the flattened view

Screen.Recording.2024-02-16.at.9.47.53.AM.mov

[mwdchang]

Per discussion, we should improve the naming in subsequent PRs. Between the usages of template, model, card, and combinations of the 3 terms it is a bit difficult to understand what is going on.