New Series Relation - Edition (#1583)

* Moved UpdateRelatedSeries from controller to SeriesService.cs

* Added 2 tests.
- UpdateRelatedSeries_ShouldDeletePrequelRelation
- UpdateRelatedSeries_ShouldNotAllowDuplicates

* Some docs and codestyle nitpicks

* Simplified tests and made easier to read

* Added 'Editions' series relation

* Missing code to properly show the relations in the UI

* Create Service for GetRelatedServices

* Added unit test. Assert Edition, Prequel and Sequel do not return parent while others do

* fixed missing userRating

* Add requested changes:
- Rename one test
- Split one test into two tests

API/Entities/Enums/RelationKind.cs

@@ -61,6 +61,16 @@ public enum RelationKind
     /// Doujinshi or Fan work
     /// </summary>
     [Description("Doujinshi")]
-    Doujinshi = 11
+    Doujinshi = 11,
+    /// <summary>
+    /// This is a UI field only. Not to be used in backend
+    /// </summary>
+    [Description("Parent")]
+    Parent = 12,
+    /// <summary>
+    /// Same story, could be translation, colorization... Different edition of the series
+    /// </summary>
+    [Description("Edition")]
+    Edition = 13
 
 }