[imp] JTable improvement to the bind method

In many of our JTable classes (see examples for contact and newsfeeds) we repeat the same code over and over json encoding some fieldsets with JRegistry. In this PR I abstract this out into the parent JTable::bind() method to make it more DRY - now all you have to do is create an class array with the array of data you wish to json encode.

It's 100% b/c with any existing code as the class var is left empty.