Export Visible Columns from spreadsheet
This commit add a button to the SpreadsheetView decorator to save currently visible array as a table. It also add a test for this feature. It should be noted that : For vtkTable "Row ID" column is not saved since it will be generated when loading the data anyway. In parallel, the "Process ID" column is saved with the name "vtkOriginalProcessIds" Holes in FieldData will be filled up with zeros Cell Type is saved as a int, not a string.