add Db class so we can reuse it in tests

Author: ylebre

lib/Db.php

@@ -0,0 +1,11 @@
+<?php
+	namespace Pdsinterop\PhpSolid;
+	
+	class Db {
+		public static $pdo;
+		public static function connect() {
+			if (!isset(self::$pdo)) {
+				self::$pdo = new \PDO("sqlite:" . DBPATH);
+			}
+		}
+	}