Issue95 2 nominal

This address https://github.com/iea-annex60/modelica-annex60/issues/95 (alias set with different nominal values).
It also adds a few other changes that are needed for OpenModelica, such as 
* an increase in the solver tolerance to avoid an assert to be triggered, and 
* a reformulation of `Buildings.Utilities.Psychrometrics.Functions.BaseClasses.TDewPoi_pW_amb` and `Buildings.Utilities.Psychrometrics.Functions.BaseClasses.pW_TDewPoi_amb` to circumvent a limitation in the OpenModelica parser.

Some warnings still persist, such as 
```
 * candidate: dp6.m_flow(nominal = 2.0)
 * candidate: fan2.m_flow_actual(nominal = fan2.m_flow_nominal)
```
as OpenModelica does not substitute the value of `fan2.m_flow_nominal` when doing the comparison.

The changes have also been merged to the master of the `Buildings` library.