Explore injecting where argument via variables

so, that `where` argument can be constructed dynamically at runtime if needed, i.e.

```
query($where: HumansCriteriaExpression) {
  Humans (where: $where) {
    select {
      id(orderBy: ASC)
      name
    }
  }
}
```
with query variables:

```
{
  "where": { 
    "appearsIn": {
      "IN": ["A_NEW_HOPE", "EMPIRE_STRIKES_BACK"]}
  }
}
```
