Rewrite bootstrapper in Python

- This was going to get too complex for bash. Only way to
  kill those scripts is before they get too complex.
- Better progress messages from bootstrapper.
- Differentiate between bootstrapper & installer
- Cleanup documentation a little bit

Dockerfile

@@ -21,8 +21,8 @@ RUN systemctl set-default multi-user.target
 STOPSIGNAL SIGRTMIN+3
 
 # Set up image to be useful out of the box for development & CI
-ENV TLJH_INSTALL_PIP_FLAGS="--no-cache-dir -e"
-ENV TLJH_INSTALL_PIP_SPEC=/srv/src
+ENV TLJH_BOOTSTRAP_DEV=yes
+ENV TLJH_BOOTSTRAP_PIP_SPEC=/srv/src
 ENV PATH=/opt/tljh/hub/bin:${PATH}
 
 CMD ["/bin/bash", "-c", "exec /sbin/init --log-target=journal 3>&1"]