This is a quick and dirty fix of issue #212.
Partially reverts previous changes from commit 5fbd1f08c4
Re-implements the change in a slightly different way.
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.