Move modal rendering using VueSimplePortal

[obulat]

Fixes

Fixes #165 by @obulat and #159 by @SaurabhAgarwala

Description

Currently, modals are rendered as child elements of help component, which makes them use styling of the parent elements. Because of this, various positioning and z-index problems arise, including the issues mentioned in #165:

• select ::after element is not clickable because it's underneath another element. So, we cannot select a language for the site.

• footer text is visible through the modal.

VueSimplePortal enables us to render the modal html to an element at the bottom of the page, outside other parent elements, and solves these issues.

Screenshots

Checklist

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  visible errors.

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[obulat]

This PR was replaced with #171 with a cleaner history.