Clarify port handling for HVAC

[DaJansenGit]

Currently, we have '_flow_master', '_flow_direction', '_flow_side', 'flow_direction', 'verbose_flow_direction' and more and a lot uf unsued functions like 'set_flow_sides'. We need to finish this unfinished work and make the process clear.

Additionally, some components like Storage are missing get_port_name() function, which is why we sometimes have 'port_unknown' in our models.