Using interface, scalar and union in shorthand type definitions

[helfer]

Right now you can define sclars, interfaces and unions just fine, but there is no easy way to attach the functions they need to them. Off the top of my head (probably incomplete):

• interface needs resolveType
• union needs members to have ofType
• scalar needs to have parseValue and serialize

[helfer]

The shorthand also doesn't support descriptions and deprecationReason.

[helfer]

One thing I'm thinking of doing to allow a workaround for these issues is to allow passing either a shorthand or a GraphQL-JS type into the schemaGenerator. That way the GraphQL-JS type definition could be used whenever the shorthand does not cut it.

[stubailo]

Yeah that's a great idea!

[helfer]

This PR implements the functionality in question via addResolveFunctionsToSchema.