Update dom.js: change NodeList to NodeList<HTMLElement>

There is a problem with code like this: 
```javascript
document.querySelectorAll('.selector')[0].style.display = 'block';
```
because `querySelectorAll` returns `NodeList` of `Element`, not `Node` https://developer.mozilla.org/en-US/docs/Web/API/element. 

I've changed `NodeList` to `NodeList<T>` and signatures of some relevant functions:
```
querySelector(selector: string): HTMLElement;
querySelectorAll(selector: string): NodeList<HTMLElement>;
```
though HTMLElement is no exactly correct (it could be any of derived classes of `Element` such as `SVGElement`, for example) I don't know better solution. 
Also, there is inconsistency with `HTMLCollection` which is collection of `Element` and will produce error with code sample.