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/src/web/i18n.py

@@ -0,0 +1,42 @@
+from quart import request, session, redirect, abort
+from quart_babel.locale import get_locale as babel_get_locale
+
+from . import web
+
+LANGUAGES = {
+    'en': 'English',
+    'de': 'Deutsch',
+    # 'fr': 'Français'
+}
+
+
+def get_locale():
+    try:
+        language = session['language']
+    except KeyError:
+        language = None
+    if language is not None:
+        return language
+
+    # check how to get the locale form for the add-on - hass.selectedLanguage
+    # logging.info("get_locale(%s)", request.accept_languages)
+    return request.accept_languages.best_match(LANGUAGES.keys())
+
+
+def get_tz():
+    return 'CET'
+
+
+@web.context_processor
+def utility_processor():
+    return dict(lang=babel_get_locale(),
+                lang_str=LANGUAGES.get(str(babel_get_locale()), "English"),
+                languages=LANGUAGES)
+
+
+@web.route('/language/<language>')
+async def set_language(language=None):
+    if language in LANGUAGES:
+        session['language'] = language
+        return redirect('../#')
+    return abort(404)