Implemented FFD interface.

This change separates the base class from the implementation of the mixed room air model.
Implemented FFD interface.

This commit adds the first versions of the base classes that will link the FFD program.
Added more connectors.

This commit also introduces the offsets for the index that couples to the FFDExchange block.
Updated convention to add dp in I/O.

This is needed as the semantics of ports does not distinguish between incoming and outgoing flow.
FFD implementation.

Revised modeling conventions, revised layout of connectors and added interface to fluid ports.
FFD implementation.

Added FFDFluidInterface.mo
FFD implementation.

Renamed QSolAbs_flow to QAbsSol_flow to use consistent names. Connected fluid port to FFD.
Renamed TestConditionalConstructions to TestConditionalConstructionsMixedAir
FFD implementation.

Started adding test cases.
Expanded loops as Dymola cannot expand them.
Revised FFD implementation.

Made surface interfaces conditional. Corrected connect statements.
Unrolled loops.
Added additional test case.
Set useFFD=false for testing.
Corrected wrong index.
Specified missing parameters.
Removed double assignment of heaPorAir.T
Removed conditional constructions.
Added pressure as a state variable.

This is required to set the port pressure and to compute change in port pressure if the room is pressurized by the HVAC system.
Revised connections to fluInt.

This version checks correctly if the FFD is replaced by a replicator.