migrate to sqlalchemy-aio.

a big refactor that:

- fixes some issues that might have happened (or not) with asynchronous
    reactions to payments;
- paves the way to https://github.com/lnbits/lnbits/issues/121;
- uses more async/await notation which just looks nice; and
- makes it simple(r?) for one extension to modify stuff from other extensions.

lnbits/extensions/example/__init__.py

@@ -1,5 +1,7 @@
 from quart import Blueprint
+from lnbits.db import Database
 
+db = Database("ext_example")
 
 example_ext: Blueprint = Blueprint("example", __name__, static_folder="static", template_folder="templates")
 

lnbits/extensions/example/views.py

@@ -1,7 +1,8 @@
 from quart import g, render_template
 
 from lnbits.decorators import check_user_exists, validate_uuids
-from lnbits.extensions.example import example_ext
+
+from . import example_ext
 
 
 @example_ext.route("/")

lnbits/extensions/example/views_api.py

@@ -10,7 +10,7 @@
 from quart import jsonify
 from http import HTTPStatus
 
-from lnbits.extensions.example import example_ext
+from . import example_ext
 
 
 # add your endpoints here
@@ -20,21 +20,9 @@ from lnbits.extensions.example import example_ext
 async def api_example():
     """Try to add descriptions for others."""
     tools = [
-        {
-            "name": "Flask",
-            "url": "https://flask.palletsprojects.com/",
-            "language": "Python",
-        },
-        {
-            "name": "Vue.js",
-            "url": "https://vuejs.org/",
-            "language": "JavaScript",
-        },
-        {
-            "name": "Quasar Framework",
-            "url": "https://quasar.dev/",
-            "language": "JavaScript",
-        },
+        {"name": "Flask", "url": "https://flask.palletsprojects.com/", "language": "Python",},
+        {"name": "Vue.js", "url": "https://vuejs.org/", "language": "JavaScript",},
+        {"name": "Quasar Framework", "url": "https://quasar.dev/", "language": "JavaScript",},
     ]
 
     return jsonify(tools), HTTPStatus.OK