Fix Modal positioning

[obulat]

Modal positioning is affected by its parent elements, so to make it render correctly, vue-simple-portal moves rendered modal html to the bottom of the page.

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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• I added tests for the changes I made (if applicable).
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  visible errors.

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[akmadian]

I'm not thrilled about adding a package, I'd like to see if there's a way to address this without the use of a package. If there isn't, or it's a deceptively difficult issue, this looks good to me :) I'm going to approve this, but I'd like you to see if there's an alternative to using a package before merging.

[obulat]

I'm not thrilled about adding a package, I'd like to see if there's a way to address this without the use of a package. If there isn't, or it's a deceptively difficult issue, this looks good to me :) I'm going to approve this, but I'd like you to see if there's an alternative to using a package before merging.

I didn't like adding a package, too, so I tried several ways of handling it today:

1. Creating a programmatic modal and passing it string value of inner html of the modal. This worked, however, the content passed inside created an additional inner div and messed up the layout of the modal (scroll and close button displayed incorrectly).
2. Creating a programmatic modal and passing it a component: this was over complicated, template rendering for components would need to have a different runtime.
3. Creating a new component at the top of the App and putting the modals there. I would also refactor the modals so that there is only one modal with the content dependent on the index of the open modal. The state of the modal (index of open modal or null) would need to be kept in the store. This seems to be the better solution, but it needs to be worked on because some modals have more content than others, and because we are using v-html in them with i18n.

At the moment, I will merge this PR with the new package, and changing the position of footer (it's currently inside section, and it should be outside it), but will look into a way of removing the package later.