Clean up old files from JTD fork.

This PR would remove files from the Just-The-Docs fork which don't appear to be necessary for our site to function, including:

1. Old Docker/devcontainer files, which appear to have only been used for development of JTD.
2. Editor/tool-specific configuration files
3. The Just-The-Docs documentation markdown files.

This is the first step towards resolving #66 (closed), giving us a more solid base to start on. After this, we can move on to actual breaking changes.

docs/ui-components/buttons.md

----
-layout: default
-title: Buttons
-parent: UI Components
-nav_order: 2
-nav_exclude: true
----
-
-# Buttons
-{: .no_toc }
-
-## Table of contents
-{: .no_toc .text-delta }
-
-1. TOC
-{:toc}
-
----
-
-## Basic button styles
-
-### Links that look like buttons
-
-<div class="code-example" markdown="1">
-[Link button](http://example.com/){: .btn }
-
-[Link button](http://example.com/){: .btn .btn-purple }
-[Link button](http://example.com/){: .btn .btn-blue }
-[Link button](http://example.com/){: .btn .btn-green }
-
-[Link button](http://example.com/){: .btn .btn-outline }
-</div>
-```markdown
-[Link button](http://example.com/){: .btn }
-
-[Link button](http://example.com/){: .btn .btn-purple }
-[Link button](http://example.com/){: .btn .btn-blue }
-[Link button](http://example.com/){: .btn .btn-green }
-
-[Link button](http://example.com/){: .btn .btn-outline }
-```
-
-### Button element
-
-GitHub Flavored Markdown does not support the `button` element, so you'll have to use inline HTML for this:
-
-<div class="code-example">
-<button type="button" name="button" class="btn">Button element</button>
-</div>
-```html
-<button type="button" name="button" class="btn">Button element</button>
-```
-
----
-
-## Using utilities with buttons
-
-### Button size
-
-Wrap the button in a container that uses the [font-size utility classes]({% link docs/utilities/typography.md %}) to scale buttons:
-
-<div class="code-example" markdown="1">
-<span class="fs-6">
-[Big ass button](http://example.com/){: .btn }
-</span>
-
-<span class="fs-3">
-[Tiny ass button](http://example.com/){: .btn }
-</span>
-</div>
-```markdown
-<span class="fs-8">
-[Link button](http://example.com/){: .btn }
-</span>
-
-<span class="fs-3">
-[Tiny ass button](http://example.com/){: .btn }
-</span>
-```
-
-### Spacing between buttons
-
-Use the [margin utility classes]({% link docs/utilities/layout.md %}#spacing) to add spacing between two buttons in the same block.
-
-<div class="code-example" markdown="1">
-[Button with space](http://example.com/){: .btn .btn-purple .mr-2 }
-[Button](http://example.com/){: .btn .btn-blue }
-
-[Button with more space](http://example.com/){: .btn .btn-green .mr-4 }
-[Button](http://example.com/){: .btn .btn-blue }
-</div>
-```markdown
-[Button with space](http://example.com/){: .btn .btn-purple .mr-2 }
-[Button](http://example.com/){: .btn .btn-blue }
-
-[Button with more space](http://example.com/){: .btn .btn-green .mr-4 }
-[Button](http://example.com/){: .btn .btn-blue }
-```