Renamed inlet and outlet to port_a and port_b

This is for #313. The renaming is done for consistency with the fluid
connectors, as it is not always known what is inlet and outlet
Added .mos script for #313.
Renamed example for #313.
Added .mos script for #313
Added flow machines and changed media.

This is for #313.
Removed flow reversal for now. For #313
Added icon for #313
Added test cases for #313
Further edited the FMU interface.

For #313