Improve an error message for non expert users

[khsrali]

Maybe we could replace

Cannot run awaitable: event loop is running but no greenback portal is available. If running in a Jupyter notebook, call load_profile() in a prior cell.
with a less technical message, like:
It looks like you are running AiiDA engine processes in the same Jupyter cell where load_profile() was called. This is not supported because the setup only takes effect from the next cell. Please call load_profile() in a separate cell before running engine processes.