Adds function to export/rebuild XML files, which are also added to src c...

...ontrol. Also makes automatic import/export of VBA code an optional setting.

New menu commands to export XML from any open file, and rebuild XML from a selected folder. XML data contains all spreadsheet objects, which are currently not accessible in the VBA-only exporter. Function saves the xlsx or xlsm as .zip and unzips to a new folder.

Sorry, not up to date with current master - if you're interested in merging in I can rebase off the current master.