Reorganize Samples

The samples have become unwieldy when running them from a browser. In particular, the drop-down lists are fixed size with no scrolling, and many of them are now just too large. I have moved all the Calculation samples up a level, and broken several categories (Basic, Chart, DateTime, Engineering, Financial, and Reader) into several pieces.

Convert-Online (now found in the Engineering category) had a number of different problems which are now resolved. It is the only member with any significant code change.

samples/Reader2/16_Handling_loader_exceptions_using_TryCatch.php

@@ -0,0 +1,15 @@
+<?php
+
+use PhpOffice\PhpSpreadsheet\IOFactory;
+use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
+
+require __DIR__ . '/../Header.php';
+
+$inputFileName = __DIR__ . '/sampleData/non-existing-file.xls';
+$helper->log('Loading file ' . pathinfo($inputFileName, PATHINFO_BASENAME) . ' using IOFactory to identify the format');
+
+try {
+    $spreadsheet = IOFactory::load($inputFileName);
+} catch (ReaderException $e) {
+    $helper->log('Error loading file "' . pathinfo($inputFileName, PATHINFO_BASENAME) . '": ' . $e->getMessage());
+}