S allius/issue395 (#399)

* add button for languages setting

* build a web module for the dashboard

- load all python module from local dir
- initialize Blueprint and Babel

* set a default key for secure cookies

* add translations to docker container

* improve translation build  

- clean target erases the *.pot
- don't modify the resurt of url_for() calls
- don't translate the language description

* translate connection table, fix icon

* build relative urls for HA ingress

* fix unit test, increase coverage

app/Dockerfile

@@ -60,6 +60,7 @@ RUN python -m pip install --no-cache-dir --no-cache --no-index /root/wheels/* &&
 # copy the content of the local src and config directory to the working directory
 COPY --chmod=0700 entrypoint.sh /root/entrypoint.sh
 COPY src .
+COPY translations ./translations
 RUN echo ${VERSION} > /proxy-version.txt \
   && date > /build-date.txt
 EXPOSE 5005 8127 10000