tools (datetime, utils): fix incorrect use of naive object: `tools.datetime.format_datetime` was expecting aware datetime objects while `tools.utils.xmpp_date` was returning naive datetime objects. A check has been added to the former one, and latter one has been modified to return aware datetime objects.

version: "3.6"
services:

  prosody:
    image: libervia/prosody:demo
    build: prosody-demo

  backend:
    image: libervia/backend:dev-demo
    build: backend-dev-demo

  web:
    image: libervia/web:dev-demo
    build: libervia-web-dev-demo