Fix #1282 Migrate spreadsheet importer to Import API
Fix #1662 Merge CSV and Spreadsheet import

Fix #1699 Add support for excel (xls and xlsx) import
Fix #1461 Spaces in header columns of edge CSV file fails to load
Fix #1661 DNA - import .CSV (from DNA software) in Gephi
Fix #1658 Export data table with large numbers in metrics rows
Fix #532 Suggestions: improvements to spreadsheet import
Fix #1248 Add support for edge kind in spreadsheet import/export
Fix #1431 CSV data missing some information

Sorry for the big merge :)