1. Added support for JSON serialization/deserialization through JSON.NET library (http://james.newtonking.com/json) :
1.1. Added ObjectExtensions.Json() method (serialization)
1.2. Added StringExtensions.Json() method (deserialization)
1.3. Added JSON unit tests for domain entities
2. Removed Silverlight 3/4 target runtimes due to absense of JSON.NET library support for these runtimes