This commit is not exhaustive, and it is a trend in this codebase to not
use StaticFiles() and instead use relative paths. This means the code
cannot run anywhere other than the source code directory, as it will not
find the files it is looking for
This adds a wrapper around uvicorn using Python. This is so the
entrypoint lnbits.server can be called on the command line, and passed
arguments like port and host. This makes lnbits feel more like a real
CLI application, and lends well to running as a service in systemd
