simplify environment variables required.

instead of multiple keys/macaroons with different permissions we request only one.
if someone wants to use lnbits with an invoice macaroon they're free to do it and
we will just fail on 'pay' methods, as before.

this also grandfathers the previous environment variables names so everything keeps
working without people having to change their setups.

in the meantime some bugs with lntxbot and c-lightning were fixed and the `requests`
dependency was eliminated because I can't organize myself into meaningful chunks of
changes.

lnbits/core/views/api.py

@@ -1,5 +1,6 @@
 import trio  # type: ignore
 import json
+import traceback
 from quart import g, jsonify, request, make_response
 from http import HTTPStatus
 from binascii import unhexlify
@@ -87,10 +88,10 @@ async def api_payments_pay_invoice():
         return jsonify({"message": str(e)}), HTTPStatus.BAD_REQUEST
     except PermissionError as e:
         return jsonify({"message": str(e)}), HTTPStatus.FORBIDDEN
-    except Exception as e:
-        print(e)
+    except Exception as exc:
+        traceback.print_exc(7)
         g.db.rollback()
-        return jsonify({"message": str(e)}), HTTPStatus.INTERNAL_SERVER_ERROR
+        return jsonify({"message": str(exc)}), HTTPStatus.INTERNAL_SERVER_ERROR
 
     return (
         jsonify(