Implement a Typescript enum for referring to a relationship type.
Example of enums in Typescript: https://www.typescriptlang.org/docs/handbook/enums.html

As for the format of each type, I suggest something like this: 
`EditionContainsWork: 10`

This can then be used when referring to relationship type id.

I suggest the file `src/client/entity-editor/relationship-editor/types.js`as its logical home.