From iterator?

Would be nice if there would be an option to build the AsyncView from an iterator, with optional progress bar of course.

Something like:

```rust
AsyncView::from_iterator(it)
```

with `from_iterator(i: I) where I: IntoIterator, V: View` or something like this?
Or even

```rust
AsyncView::fold_from_iter(it, ListView::new(), |accu, elem| { accu.add_child("", elem); accu });
```

where the closure folds over the `ListView` and `elem` as element from the iterator?