feat($state): make state data inheritance prototypical

[chrislambe]

Modify state data inheritance to use prototypical inhertiance rather than Angular's extend method to enable more flexibility in handling state data.

Justification

I'm currently working on a project that implements Material Design via Angular Material. We've implemented a global FAB by attaching information about what the FAB should do to the state definition. For example:

angular.module('MyMaterialDesignProject')
  .config(function($stateProvider) {
    $stateProvider
      .state('foo', {
        url: '/foo',
        data: {
          primaryAction: {
            onClick: function($state) {
              $state.go('foo.bar');
            }
          }
        }
      })
      .state('foo.bar', {
        url: '/bar'
      });
  });

When we arrive at foo.bar we need to be able to tell if data.primaryAction is defined as part of the foo.bar state definition or if it's inherited. If it's inherited we (maybe) don't want to display the FAB.

Risk of breaking change

Any dev who has implemented a test to determine the availability of a data property using data.hasOwnProperty('foo') rather than something like 'foo' in data is at risk of having their app stop functioning as they expect.

[nateabele]

@christopherthielen Obviously we'll want to use inherit() but I am fundamentally down with this. Any objection?

[chrislambe]

Switched to using inherit().

[christopherthielen]

I totally thought we were already doing it this way, hah. 👍

@chrislambe
FYI I use data for metadata the entire tree of states cares about, but I've been plopping non-inherited metadata directly on the state declarations, e.g.,

.state('admin', {
 url: '/admin',
 dsr: true, // <- plop
 data: {
  roles: ['ADMIN']
 } 
}```

[chrislambe]

@christopherthielen Oh, interesting. That's helpful, thanks!