migrate from flask to quart.

also remove all flaskiness from static file serving.
and reference all vendored scripts on the base tempĺate for simplicity.

lnbits/extensions/example/views.py

@@ -1,4 +1,4 @@
-from flask import g, render_template
+from quart import g, render_template
 
 from lnbits.decorators import check_user_exists, validate_uuids
 from lnbits.extensions.example import example_ext
@@ -7,5 +7,5 @@ from lnbits.extensions.example import example_ext
 @example_ext.route("/")
 @validate_uuids(["usr"], required=True)
 @check_user_exists()
-def index():
-    return render_template("example/index.html", user=g.user)
+async def index():
+    return await render_template("example/index.html", user=g.user)