docs: add dark and light theme

Basically contains most changes from:
SensorsIot#338

* Dark and light modes
* Always expand left-navigation folders, improving usability

.github/workflows/main.yml

@@ -9,10 +9,10 @@ jobs:
     name: Deploy docs
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout master
-        uses: actions/checkout@v1
-
-      - name: Deploy docs
-        uses: mhausenblas/mkdocs-deploy-gh-pages@master
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.x
+      - run: pip install mkdocs-material
+      - run: pip install mkdocs-git-revision-date-localized-plugin
+      - run: mkdocs gh-deploy --force

mkdocs.yml

@@ -1,10 +1,28 @@
 site_name: IOTstack
 site_description: 'Docker stack for getting started on IOT on the Raspberry PI'
+
+# Repository
+repo_url: https://github.com/SensorsIot/IOTstack
+repo_name: SensorsIot/IOTstack
+edit_uri: "https://github.com/SensorsIot/IOTstack/edit/master/"
+
 theme:
   name: material
-plugins:
-  - search
-# - awesome-pages
+  palette:
+    - scheme: default
+      toggle:
+        icon: material/weather-sunny
+        name: Switch to dark mode
+    - scheme: slate
+      toggle:
+        icon: material/weather-night
+        name: Switch to light mode
+  features:
+    - tabs
+    - navigation.expand
+  plugins:
+    - search
+    - git-revision-date-localized
 markdown_extensions:
+  - admonition
   - pymdownx.superfences
-repo_url: https://github.com/SensorsIot/IOTstack