Edited derive and define Classes

When you don't need to use a constructor is better don't pass anything
in constructor parameter.

Example before:
// normal Class
var a = WinJS.Class.define(constructor, instanceMembers, staticMembers);
// without constructor
var b = WinJS.Class.define(null, instanceMembers, staticMembers);

Example now:
// normal Class
var a = WinJS.Class.define(constructor, instanceMembers, staticMembers);
// without constructor
var b = WinJS.Class.define(instanceMembers, staticMembers);