All 1-character strings converted to primitives

"b" + "r" now changed to 'b' + 'w'.  It's more straight-forward, and may cause perfomance improvements - character primitives allocation is faster and less expensive than string creation.

Mage/src/main/java/mage/abilities/keyword/ProwlAbility.java

@@ -167,7 +167,7 @@ public class ProwlAbility extends StaticAbility implements AlternativeSourceCost
             ++numberCosts;
         }
         if (numberCosts == 1) {
-            sb.append(" ").append(remarkText);
+            sb.append(' ').append(remarkText);
         }
 
         return sb.toString();