CleanUp Cache namespace

- Introduce enum "Duration"
- Introduce enum "Type"
- Move "Cache\Cache" to "BaseCache"

src/Core/Cache/Duration.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Friendica\Core\Cache;
+
+/**
+ * Enumeration for cache durations
+ */
+abstract class Duration
+{
+	const MONTH        = 2592000;
+	const HOUR         = 3600;
+	const HALF_HOUR    = 1800;
+	const QUARTER_HOUR = 900;
+	const MINUTE       = 60;
+	const WEEK         = 604800;
+	const INFINITE     = 0;
+	const DAY          = 86400;
+	const FIVE_MINUTES = 300;
+}