ENH: default value of HideFromEditors flag set to 0

This change will cause new mrml nodes to not be hidden
from editors by default, developers subclassing
vtkMRMLNode will need to specify the following in
constructors to over ride this behaviour:
this->HideFromEditors = 1;

MRML Core nodes that should be hidden in the Data module
were updated to stay hidden.

From the Slicer Roadmap for 4.4:
https://www.slicer.org/slicerWiki/index.php/Roadmap#4.4

Issue #2906



git-svn-id: http://svn.slicer.org/Slicer4/trunk@22937 3bd1e089-480b-0410-8dfb-8563597acbee