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.
Corrected error in FFDExchange and added test case for FFDExchange.
Updated I/O conventions.
Implemented mass balance and propagated volume and initial conditions.
Declared yFixed and assigned values.
Corrected wrong output variable name.
Changed variable names and cleaned up code.