Add the Config class

Add a Config class for storing configuration values such as the
Glassboxx username, password and vendor ID.

src/Glassboxx/Config.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Opdavies\Glassboxx;
+
+class Config
+{
+    /** @var int $vendorId */
+    private $vendorId;
+
+    /** @var string $username */
+    private $username;
+
+    /** @var string $password */
+    private $password;
+
+    public function __construct(
+		int $vendorId,
+        string $username,
+        string $password
+	) {
+        $this->password = $password;
+        $this->username = $username;
+        $this->vendorId = $vendorId;
+    }
+
+    public function getPassword(): string
+    {
+        return $this->password;
+    }
+
+    public function getUsername(): string
+    {
+        return $this->username;
+    }
+
+    public function getVendorId(): int
+    {
+        return $this->vendorId;
+    }
+}