Support flattening the data

Nobody has claimed this yet.

This task depends on https://github.com/linksplatform/Data.Doublets.Gql/issues/8

It can also be useful to use resolver to flatten the structure:
```gql
{
from_string
to_string
}
```
instead of
```gql
{
from { string }
to { string }
}
```
It will make possible to do something like this with aliases:
```gql
{
TrackName: from_string
DownloadsCount: to_string
}
```
And the user will be able to get JSON with this structure:
```json
{
"TrackName": "GANGNAM STYLE",
"DownloadsCount": "4163140300"
}
````

But, this can overcomplicate the API, so https://github.com/APIs-guru/graphql-lodash can be a better client-side solution.

Start by reading the dependency in issue #8, then compare the nested and flattened GraphQL examples in this issue with the graphql-lodash alternative. Done requires deciding whether resolver-based flattening belongs in the API and, if so, supporting the shown aliases and JSON-shaped result.

Written by the indexing model from the issue text.