Custom EPW time intervals

[dhblum]

This issue is to provide provide the capability to use custom EPW files with time intervals different than 1 hour. MPCPy assumes a 1 hour time interval when creating the weather exodata object timestamps. This development will instead detect the time interval of the EPW file submitted, and adjust the exodata object accordingly.

Note that EPW files adopt an "hour-ending" format, meaning for instance that Hr 1 values represent a value from Hr 0 to Hr 1. To align better with other simulation practices, including Modelica, EPW file values are shifted one time step back so that the exodata weather object adopts an "hour-starting" format. The same will apply in this issue's development.

[mwetter]

@dhblum Please see also
https://github.com/ibpsa/modelica-ibpsa/tree/master/IBPSA/Resources/src/convertEPW
which is used by Buildings as well.