S allius/issue387 (#388)

* add optional java script to fetch data regullary

* change file extension to `html.j2` for templates

* fix route for fetch data

- for running in iframes (e.g. HA ingress) we must
  use relative path in the URLs

* increase test coverage

* remove unused statements

app/Makefile

@@ -10,7 +10,7 @@ APP=.
 SRC=$(APP)/src
 # Folders for Babel translation
 BABEL_INPUT_JINJA=$(SRC)/web/templates
-BABEL_INPUT= $(foreach dir,$(BABEL_INPUT_JINJA),$(wildcard $(dir)/*.html)) \
+BABEL_INPUT= $(foreach dir,$(BABEL_INPUT_JINJA),$(wildcard $(dir)/*.html.j2)) \
 
 BABEL_TRANSLATIONS=$(APP)/translations