Added functionality to save constants as datasets defined in the layout ...

Added feature to save constant information in the xml layout into datasets. It now allows to save a constant string, int or 1d array of integers separated by a comma, and float or 1d array of floats to a dataset. This is consistent with the format for saving constants to hdf attributes.  
The constant hdf5 attribute code was not affected with this change, new functions were added for constant datasets.

Minor update to  ADApp/Db/NDFileHDF5_settings.req to save/restore the XMLFileName for autosave