Silverlight has been deprecated with CRM 2013 and 2015 as Microsoft is no longer developing it.
The replacement would be to use straight HTML web resources with JQuery and other similar tools.
Check out SparkleXRM at http://www.sparklexrm.com/s/default.html for a pretty good replacement for Silverlight that allows you to write C# code, that then compiles to JavaScript that you can load
to CRM as a web resource.