Added Experimtal/AirPTDecoupled.

This is for #21. This medium has been added to allow numerical experiments on the large air-based systems in the Buildings library in order to see what that ddifference is between this medium and the new (yet to be implemented) air model.
Simplified Media.

This is for #21.
Simplified Media.

This is for #21.
Revised media implementation.

This is for #21.
Made new structure for media.
Note that Media.Water still has a constant density, this will need to
be changed.
Also, Media.Air is using the ideal gas law, this should be changed to
an incompressible medium.
Changed medium from Annex60.Experimental.AirPTDecoupled to Annex60.Media.Air
Added test models for AirPTDecoupled, and move it to Experimental.Media package.

This is for #21.
Set p_default=3 bar as this is used to initialize the pressure.

This is for #21.
Corrected wrong within statement.
Changed air model to be incompressible.

This is for #21. This change also implements the specificEntropy and the setState_psX functions.
Added pressure boundary condition.
Added documentation.

This is for #21.
Added missing package.mo file.

This is for #21.
Revised air medium.

This is for #21.
Fixed error in pressure function.

This is for #21. This function needs to return p and not p_reference.
Changed p_reference to p in functions.

This is for #21. It is needed for
 Annex60.Fluid.MixingVolumes.Examples.MixingVolumeInitialization
to translate.
Changed cpWatLiq for consistency with Water.mo. Removed phi in base properties.
Preliminary revision of water model.
Revised specificInternalEnergy and did other revisions.

This is for #21.
Added functions for density and kinematic viscosity.
Revised water (for #21).