General: revert to using a big entry file, with only the Logo mov… (#57)

* General: move VaultPress class back to main plugin file

Partially reverts #16

* Logo: move to separate file.

This will avoid us using PHP5.3+ syntax in the plugin's entry file,
thus not fataling PHP 5.2 sites.

class-jetpack-logo.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * Jetpack Logo for use on dashboard pages.
+ *
+ * @since 2.1.0
+ *
+ * @package VaultPress
+ */
+
+use Automattic\Jetpack\Assets\Logo;
+
+/**
+ * Jetpack Logo Class.
+ */
+class Jetpack_Logo {
+	/**
+	 * Constructor.
+	 */
+	public function __construct() {
+	}
+
+	/**
+	 * Display a Jetpack Logo.
+	 */
+	public function output() {
+		$logo = new Logo();
+		return $logo->render();
+	}
+}