Add default option to not automatically generate cleaver route names

[jordanh]

Take this call signature:

export function createGetByIdRoute(routeBasename, acceptedKeys, getByIdPromise,
  modelKeyGetter = defModelKeyGetter,
  modelIdKey = defModelIdKey) { /* ... */ }

And this invocation:

  createGetByIdRoute(
    'users',
    ['createdAt', 'updatedAt', 'userId', 'email',
     'emailVerified', 'picture', 'name', 'nickname',
     'identities', 'loginsCount', 'blockedFor'],
    async (id) => CachedUser.getUserByUserId(id),
    (model, id) => model[id],
    'userId'
  )

It will generate a route called usersById which will surprise users if they aren't expecting it. By default, I don't think we should do this. Instead, after implementing #3, we should provide a default option that disables this behavior and instead enable this behavior only when the individual route generators are called from createRoutes().