Suggestion: Make `amOnPage()` wait for JavaScript to finish by default

[ThomasLandauer]

Starting point: Everybody always wants JavaScript to finish, before performing any action/assertion on the page, right?
At least my usual pattern is:

$I->amOnPage('/');
$I->waitForJS('return document.readyState === "complete";', 5); // https://gist.github.com/pastuhov/43674b195dc293ffd847

So I thought about ways to simplify this. My first idea was to introduce a new method, something like waitForJSToComplete().

But now, I think it's even better to include this in amOnPage(), by introducing a second parameter:

public function amOnPage($page, bool $waitTillJSIsComplete = true): void

This would be a BC break.

[rhuijts]

That would be a nice option to have, but sometimes I only need the DOM to be loaded for my test. Other times I also need to wait for animations to complete. What about a more generic function to wait for a JavaScript event?

$I->amOnPage('/');
$I->waitForEvent('DOMContentLoaded');
// Assert things in the DOM
$I->waitForEvent('load');
// Now document.readyState is "complete"
$I->waitForEvent('myScrollAnimationIsDone');
// Assert my buttons are clickable

Alternatively, perhaps just an amOnLoadedPage() function, to avoid breaking BC.