Massive code cleanup

- Avoid fighting import cycles using a factory function
- Collapse useless subpackages into simple modules
- Move flask plugins / infrastructure in own module
- Refactor how blueprints are used to localize information about
  URL routing to app factory

snikket_web/infra.py

@@ -0,0 +1,40 @@
+import itertools
+import typing
+
+import quart.flask_patch  # noqa:F401
+from quart import (
+    current_app,
+    request,
+)
+
+import flask_babel
+
+from . import prosodyclient
+
+
+client = prosodyclient.ProsodyClient()
+client.default_login_redirect = "main.login"
+
+babel = flask_babel.Babel()
+
+
+@babel.localeselector  # type:ignore
+def selected_locale() -> str:
+    return request.accept_languages.best_match(
+        current_app.config['LANGUAGES']
+    )
+
+
+def flatten(a: typing.Iterable, levels: int = 1) -> typing.Iterable:
+    for i in range(levels):
+        a = itertools.chain(*a)
+    return a
+
+
+def init_templating(app: quart.Quart) -> None:
+    app.template_filter("repr")(repr)
+    app.template_filter("format_datetime")(flask_babel.format_datetime)
+    app.template_filter("format_date")(flask_babel.format_date)
+    app.template_filter("format_time")(flask_babel.format_time)
+    app.template_filter("format_timedelta")(flask_babel.format_timedelta)
+    app.template_filter("flatten")(flatten)