Urql support

[mxstbr]

I mainly just copied the react-apollo plugin and rewrote the generated code to use the urql API, which differs from the react-apollo and react-apollo-hooks a bit.

• Generate hooks
• Generate components
• Fix options
• Test whether generated code actually works

Closes #1575

[mxstbr]

Testing this in our project, this fails because Urql.Use<Query|Mutation|Subscription>Args is not exported from urql. /cc @kitten

[mxstbr]

Blocked by urql-graphql/urql#235, otherwise this is almost ready pending some cleanup

That PR was merged, this is basically ready! Note that I have only tested hooks in our project, as we don't use any components.

[dotansimha]

@mxstbr that's looks great.
Note that the base client-side also has configuration for noGraphQlTag that precompile the GraphQL operations into a DocumentNode during generation, so I think we need to make sure it's compatible with urql (I guess it should work, but worth a check).

[mxstbr]

Note that components support currently fails with this error:

TypeScript error: Type '{ variables: QueryVariablesName; requestPolicy?: "cache-first" | "cache-only" | "network-only" | "cache-and-network" | undefined; query: any; }' is missing the following properties from type 'QueryHandlerProps': client, children, key  TS2739

I am not sure how to resolve that. It's caused by Urql.Query expecting more props than we provide to the custom components.

[mxstbr]

Fixed component generation in the latest commit, pending the publication of a new version of urql with this patch applied urql-graphql/urql#236 this works great! 💯

@dotansimha this should be ready to ship?!?!

[dotansimha]

Thanks @mxstbr ! Looks great.
(btw, you can test and use it now, before the next stable release, because we are publishing an alpha version per each commit)