Flask extensions are loaded in a way that makes them easily reusable by blueprints.
In this commit we are also adding `environs` to manage .env and settings:
breaking changes!
- FLASK_APP=lnbits.app
- LNBITS_ALLOWED_USERS needs to be empty now to allow all users (NOT "all")
The `LNBITS_ALLOWED_USERS` env var can be used to limit access
to the application to some uuids only. "all" gives open access.
UUIDs should be comma separated.
