Consolidate types

[avenmia]

This issue is to consolidate types in order to reduce duplication.

For example, as part of the the recent "display pol.is surveys based on demographics questions" feature, I had to update the answer type in several places to include an ID.

ans: { id: string; val: string }

Ideally, this type would be declared in one spot.

interface Answer {
  id: string;
  val: string;
}

...
ans: Answer

For this issue, document places where types can be consolidated and update the types

References:
https://blog.logrocket.com/types-vs-interfaces-typescript/
https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#differences-between-type-aliases-and-interfaces