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

ha_addons/Makefile

@@ -87,6 +87,7 @@ SRC_FILES := $(wildcard $(SRC_PROXY)/*.py)\
  $(wildcard $(SRC_PROXY)/cnf/*.toml)\
  $(wildcard $(SRC_PROXY)/gen3/*.py)\
  $(wildcard $(SRC_PROXY)/gen3plus/*.py)\
+ $(wildcard $(SRC_PROXY)/utils/*.py)\
  $(wildcard $(SRC_PROXY)/web/*.py)\
  $(wildcard $(SRC_PROXY)/web/templates/*.html.j2)\
  $(wildcard $(SRC_PROXY)/web/static/css/*.css)\