Move files, complete PHP migration

The application works the same way as the F# version

src/lib/Domain/RequestAction.php

@@ -0,0 +1,21 @@
+<?php declare(strict_types=1);
+
+namespace MyPrayerJournal\Domain;
+
+/**
+ * An action taken on a prayer request
+ */
+enum RequestAction: string
+{
+    /** The request was created */
+    case Created = 'Created';
+
+    /** The request was marked as having been prayed for */
+    case Prayed = 'Prayed';
+
+    /** The request was updated */
+    case Updated = 'Updated';
+
+    /** The request was marked as answered */
+    case Answered = 'Answered';
+}