Pickadate v5.0.0 Doesn't Work in IE11 (Multiple Issues)

### Issue Summary
IE11 has multiple issues with rendering / activating Pickadate v5.0.0 Alpha 2. I know IE11 sucks by default, but a lot of companies will probably have to support it until the end of time.

**This seems to be a three part issue:**

1. The official [pickadate demo](https://amsul.ca/pickadate.js/v5/docs/introduction) does not render in IE11 at all. Instead, there's a blank space where the datepicker is supposed to be and this message in the console:

I've found you can get the datepicker to render / activate by adding the following polyfills:
```html

```

2. You can't change the month in any browser. It looks like pickadate triggers a form submission every time any calendar item is clicked. However, if you specify the datepicker's button types, you can change the month:
```js
document.querySelectorAll('button').forEach(function(el) {
el.setAttribute("type", "button");
});
```

3. Datepicker won't close or change the date in the input field that triggered it. Zero errors show up in the Chrome Console after making the fixes above.

### Codepen Test
I've added a test to Codepen to demonstrate the third issue. This test uses Bootstrap, Pickadate v5.0.0 Alpha 2, IE11 polyfills, and some basic init code:
https://codepen.io/callaginn/pen/QPdxGO

_Note: You'll need to open it in debug mode to view it in IE11._