Plugin: keyboard shortcut to add all fields

Related: https://github.com/graphql/graphiql/issues/75

I would love to see a button, or a key combination that will add/autocomplete all direct fields of the current object. Complex fields will be autocompleted to {}, that will need to be manually fileld out.

Example:
```
Type Person with fields id, name, groups, teams
Type Group with fields id, name, people
Type Teams with fields id, name, people
```

Typing
```
query {
people {

}
}
```

becomes
```
query {
people {
id
name
groups(page: null , page_size: null) {
}
teams(page: null , page_size: null) {
}
}
}
```

Also plus if the complex subtypes are added at the end