Attempt to fix issues caused by multiple enabled pw-module installers

Author: teppokoivula

composer.json

@@ -17,6 +17,9 @@
         "hari/pw-module": "^1.0.0"
     },
     "autoload": {
+        "psr-0": {
+            "PW\\Composer\\": "src/"
+        },
         "psr-4": {
             "wireframe\\": "src/"
         }

src/PW/Composer/SystemInstaller.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace PW\Composer;
+
+/**
+ * Compatibility layer for the PW\Composer\SystemInstaller class from hari/pw-module
+ *
+ * wireframe-framework/processwire-composer-installer and hari/pw-module are not fully compatible,
+ * which means that when wireframe-framework/processwire-composer-installer is enabled, we need to
+ * disable hari/pw-module.
+ */
+class SystemInstaller extends \wireframe\ComposerInstaller\BaseInstaller {}