feat: add a switch to toggle light/dark theme

Add script for restoring preferred theme setting.
Update config for newer `mkdocs-material`.
Use native `mkdocs-material` styles where possible.

Closes: #45 #63

Dockerfile

@@ -1,6 +1,7 @@
 # Install the base requirements for the app.
 # This stage is to support development.
 FROM python:alpine AS base
+RUN apk add --no-cache g++
 WORKDIR /app
 COPY requirements.txt .
 RUN pip install -r requirements.txt