[TS] Use Typescript string enum for enums

[clayne11]

As of Typescript 2.4 Typescript supports string enums. Use these instead of union string types for enums.

Example:

// old
export type Test = "FOO" | "BAR" | "FOOBAR"

// suggested
export enum Test = {
  FOO = "FOO",
  BAR = "BAR",
  FOOBAR = "FOOBAR"
}

This will allow us to import and use the enums within our apps rather than having to create an identical enum.