Added a GreaterThan validator based upon the EqualTo

Refactored EqualTo validator by pulling common comparison validation code to an abstract base class and added GreaterThan validator based upon the base.  

Note: I added a GreaterThan jQuery validator to support the DataAnnotation validator.  These need to be added to the NuGet package:  

jquery.validate.additional-methods.js 
jquery.validate.unobtrusive.additional-methods.js