Rename and re-organise custom modules

- Rename `opd_talks` to `opdavies_talks`
- Rename `custom` to `opdavies_blog`

web/modules/custom/opdavies_blog/opdavies_blog.module

@@ -0,0 +1,18 @@
+<?php
+
+/**
+ * @file
+ * Custom module.
+ */
+
+declare(strict_types=1);
+
+use Symfony\Component\Finder\Finder;
+
+$finder = Finder::create()
+  ->in(__DIR__ . DIRECTORY_SEPARATOR . 'hooks')
+  ->name('/.[php|inc]$/');
+
+foreach ($finder as $file) {
+  include $file->getPathname();
+}