Add FileManager, File cleanup, Logger

src/main/kotlin/nl/astraeus/persistence/Logger.kt

@@ -0,0 +1,8 @@
+package nl.astraeus.nl.astraeus.persistence
+
+object Logger {
+  var debug: (String) -> Unit = { println("DEBUG: $it") }
+  var info: (String) -> Unit = { println("INFO: $it") }
+  var warn: (String) -> Unit = { println("WARN: $it") }
+  var error: (String) -> Unit = { println("ERROR: $it") }
+}