bot: add color change command

PluralKit.Core/Utils.cs

@@ -21,6 +21,12 @@ namespace PluralKit
             if (str.Length < maxLength) return str;
             return str.Substring(0, maxLength - ellipsis.Length) + ellipsis;
         }
+
+        public static bool IsLongerThan(this string str, int length)
+        {
+            if (str != null) return str.Length > length;
+            return false;
+        }
     }
 
     public static class Emojis {