add parsing of OpenDocument spreadsheets (ods files). added a NUnit test for it.
also added a function to parse xlsx files into a DataTable, also with NUnit test.
remove a logging statement
Parsing OpenDocument spreadsheet: resolve bug with consecutive cells with same values
merge from ~tpokorra/openpetraorg/dev0002675_import_ods_files (backport!)
This is about importing from Open Document Spreadsheet file with extension ods