ENH: Added schema file support for defining table column properties

Data type, default value, long name, description, unit, and any number of custom properties can now be defined for each column in a vtkMRMLTableNode.

Long name, description, and unit are shown in table view.
Data type is used for creating numeric arrays when reading the table.csv
Default value is used for initializing values in new rows.

Properties are stored in a schema file, which is a CSV or TSV file with the composite file extension .schema.csv (or .schema.csv or .schema.txt) with the same base filename as the data table file.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@26052 3bd1e089-480b-0410-8dfb-8563597acbee