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/lnurlp/views.py

@@ -3,7 +3,7 @@ from http import HTTPStatus
 
 from lnbits.decorators import check_user_exists, validate_uuids
 
-from lnbits.extensions.lnurlp import lnurlp_ext
+from . import lnurlp_ext
 from .crud import get_pay_link
 
 
@@ -16,11 +16,17 @@ async def index():
 
 @lnurlp_ext.route("/<link_id>")
 async def display(link_id):
-    link = get_pay_link(link_id) or abort(HTTPStatus.NOT_FOUND, "Pay link does not exist.")
+    link = await get_pay_link(link_id)
+    if not link:
+        abort(HTTPStatus.NOT_FOUND, "Pay link does not exist.")
+
     return await render_template("lnurlp/display.html", link=link)
 
 
 @lnurlp_ext.route("/print/<link_id>")
 async def print_qr(link_id):
-    link = get_pay_link(link_id) or abort(HTTPStatus.NOT_FOUND, "Pay link does not exist.")
+    link = await get_pay_link(link_id)
+    if not link:
+        abort(HTTPStatus.NOT_FOUND, "Pay link does not exist.")
+
     return await render_template("lnurlp/print_qr.html", link=link)