[Enh]: GT Form Tokens should Flow

Before, if there were many multiple options or to-many relation items, they would often run off the screen and get clipped. 

After, they flow down to stay within the container horizontally

source/Magritte-GToolkit/MATokenSelectorElement.class.st

@@ -110,8 +110,8 @@ MATokenSelectorElement >> relationDescription: anObject [
 MATokenSelectorElement >> tokenContainer [
 	tokenContainer ifNotNil: [ ^ tokenContainer ].
 
-	^ tokenContainer := BrHorizontalPane new
+	^ tokenContainer := BrHorizontalFlow new
 		vFitContent;
-		hFitContent;
+		hMatchParent;
 		yourself
 ]