phpstan support (#250)

* phpstan v1 + workflow

* Fix intend

* More fixes

* Update phpstan.neon

* phpstan level 2

* Move errors ignoring into phpstan.neon

* phpstan level 3

* Don't ignore templates folder

* Something from level 4

* Update phpstan.neon

system/src/CsrfToken.php

@@ -25,7 +25,7 @@ class CsrfToken
 	 *
 	 * @access public
 	 * @static true
-	 * @return void
+	 * @return string
 	 **/
 	public static function create(bool $return = false): string {
 		$input = '<input type="hidden" name="csrf_token" value="' . self::get() . '" />';