Migrate to Docusaurus (#329)

* docs: initial migration to docusaurus

* website: add custom font, update blurbs and icons

* website: update splash

* root: update links to docs

* flows: use .pbflow extension so docusaurus doesn't mangle the files

* e2e: workaround prospector

* Squashed commit of the following:

commit 1248585dca
Author: Jens Langhammer <jens.langhammer@beryju.org>
Date:   Sun Nov 15 20:46:53 2020 +0100

    e2e: attempt to fix prospector error again

commit 1319c480c4
Author: Jens Langhammer <jens.langhammer@beryju.org>
Date:   Sun Nov 15 20:41:35 2020 +0100

    ci: install previous python version for upgrade testing

* web: update accent colours and format

* website: format markdown files

* website: fix colours for text

* website: switch to temporary accent colour to improve readability

* flows: fix path for TestTransferDocs

* flows: fix formatting of tests

website/docusaurus.config.js

@@ -0,0 +1,78 @@
+module.exports = {
+    title: "passbook",
+    tagline: "The authentication glue you need.",
+    url: "https://passbook.beryju.org",
+    baseUrl: "/",
+    onBrokenLinks: "throw",
+    favicon: "img/logo.png",
+    organizationName: "BeryJu",
+    projectName: "passbook",
+    themeConfig: {
+        navbar: {
+            title: "passbook",
+            logo: {
+                alt: "passbook logo",
+                src: "img/logo.svg",
+            },
+            hideOnScroll: true,
+            items: [
+                {
+                    to: "docs/",
+                    activeBasePath: "docs",
+                    label: "Docs",
+                    position: "left",
+                },
+                {
+                    href: "https://github.com/beryju/passbook",
+                    label: "GitHub",
+                    position: "right",
+                },
+            ],
+        },
+        footer: {
+            links: [
+                {
+                    title: "Docs",
+                    items: [
+                        {
+                            label: "Documentation",
+                            to: "docs/",
+                        },
+                        {
+                            label: "Installations",
+                            to: "docs/installation/index",
+                        },
+                    ],
+                },
+                {
+                    title: "More",
+                    items: [
+                        {
+                            label: "GitHub",
+                            href: "https://github.com/beryju/passbook",
+                        },
+                    ],
+                },
+            ],
+            copyright: `Copyright © ${new Date().getFullYear()} BeryJu.org. Built with Docusaurus.`,
+        },
+        colorMode: {
+            respectPrefersColorScheme: true,
+        },
+    },
+    presets: [
+        [
+            "@docusaurus/preset-classic",
+            {
+                docs: {
+                    sidebarPath: require.resolve("./sidebars.js"),
+                    editUrl:
+                        "https://github.com/beryju/passbook/edit/master/website/",
+                },
+                theme: {
+                    customCss: require.resolve("./src/css/custom.css"),
+                },
+            },
+        ],
+    ],
+};