Need a way to exclude unreferenced components from the getLatest snapshot

[KRyan]

Scenario 1: A user adds 100 atmentions, then deletes them all. The 100 atmentions are still in the document, breaking single-blob file read and compromising boot perf.
Implication: We need a way to mark a component to indicate that it should not be included in the getLatest snapshot.

Scenario 2: The user views a Fluid Component in OWA, but that component was removed. However, the user can still use some UI to see the component in the state it was created.
Implication: We cannot truly delete a component.

Short term, we could use a convention to prevent SP from deleting a component.

Longer term, we should design an app load template experience.

@vladsud @cosmincatrinescu @ZeguangWu @aboktor

[vladsud]

#1096 "Design: Creation Flow / Singletons" should address this and not require new work

[SamBroner]

Addressed by other issue