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/Basic1/17a_Html.php

@@ -0,0 +1,17 @@
+<?php
+
+use PhpOffice\PhpSpreadsheet\Writer\Html;
+
+require __DIR__ . '/../Header.php';
+$spreadsheet = require __DIR__ . '/../templates/sampleSpreadsheet.php';
+$spreadsheet->getProperties()->setTitle('Embedded images');
+
+$helper->write(
+    $spreadsheet,
+    __FILE__,
+    ['Html'],
+    false,
+    function (Html $writer): void {
+        $writer->setEmbedImages(true);
+    }
+);