Updated page metadata to include in tour

The Self Types page wasn't being included in the tour TOC, but was being referenced by the tour pages before and after it, Compound Types and Implicit Parameters respectively. Updated the page metadata to include it in the tour, and fix the other tags.

Author: bradfordlynch

_tour/self-types.md

@@ -4,12 +4,15 @@ title: Self-type
 
 discourse: true
 
-tutorial: scala-tour
-categories: tour
+partof: scala-tour
+
 num: 25
 next-page: implicit-parameters
 previous-page: compound-types
+topics: self-types
 prerequisite-knowledge: nested-classes, mixin-class-composition
+
+redirect_from: "/tutorials/tour/self-types.html"
 ---
 Self-types are a way to declare that a trait must be mixed into another trait, even though it doesn't directly extend it. That makes the members of the dependency available without imports.