LDDTool: XMLSchema Fix Null In Import Cleanup

[jshughes416]

LDDTool general cleanup
MasterDOMInfoModel - move test on testTrue outside of loop
DOMDataType - setting this.nsTitle is not needed since it is set by this.setIdentifier
DMDocument - added "exit" message
XML4LabelSchemaDOM - get info for XML schema namespace declaration - add pds (common) as default
WriteDOMSchematron - get info for XML schema namespace declaration - add pds (common) as default
LDDDOMParser - added helpful comments.

[rchenatjpl]

As with #77, it's hard to know what to test.

[jordanpadams]

@jshughes416 please help out here?

[rchenatjpl]

Yes, I'll say this one is fixed as well, though I don't understand the problem or the solution.

[jordanpadams]

@rchenatjpl I think this is under the hood leading to outputs

[jshughes]

This is the issue where null was in the output file name PDS4_GEOM_null_1700. Here is the test file.

PDS4_IMG_IngestLDD_190928_changeExtensionToXML.txt