PHP8

The latest version of PHP is PHP8, and there were many changes that webERP needed to take account of.

PHPExcel is no longer maintained and is not PHP8 compatible. The proposal is that we move to PHPSpreadsheet instead. https://github.com/timschofield/webERP/wiki/Spreadsheet

TCPDF is no longer maintained and is not PHP8 compatible. The proposal is that we adopt DomPDF instead. https://github.com/timschofield/webERP/wiki/TCPDF