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/pages.py

@@ -0,0 +1,16 @@
+from quart import render_template
+from .wrapper import url_for
+
+from . import web
+
+
+@web.route('/')
+async def index():
+    return await render_template(
+        'index.html.j2',
+        fetch_url=url_for('web.data_fetch'))
+
+
+@web.route('/page')
+async def empty():
+    return await render_template('empty.html.j2')