Initial import from Alltube app

Removed dependency on Config and LocaleManager classes
Avoid using generic exceptions

classes/exceptions/PopenStreamException.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace Alltube\Library\Exception;
+
+/**
+ * Could not open popen stream.
+ */
+class PopenStreamException extends AlltubeLibraryException
+{
+    /**
+     * @var string Error message
+     */
+    protected $message = 'Could not open popen stream.';
+}