Fix select controls to handle groups in reactions

[max-scopp]

See #1513

[ovidiuch]

Looks pretty good! A few changes and a useSelect test and we can merge it. If you find creating the test confusing let me know and I can help.

[ovidiuch]

Just realized this also needs attention:

react-cosmos/packages/react-cosmos-renderer/src/fixture/useSelect/useCreateFixtureState.ts

Line 39 in f442f14

}, [String(args.options), defaultValue, selectName, setFixtureState]);

Stringifying the options list is a trick make the options list a dependency of that hook without invalidating the effect on every render even if the options list is identical. But stringifying an array of string is the equivalent of array.join(',') and this won't work anymore when the options can contain group objects. So this needs to be changed to JSON.stringify(args.options) or something else.

[ovidiuch]

@max-scopp are you still interested in getting this merged? I can help if needed :).

[ovidiuch]

Figured out I had write access on the fork so I made the changes myself 😉