Removed isolated scope, use inherited scope values

Isolated scope is not really needed, and if requested, can conflict with other directives:

```html
Error: [$compile:multidir] Multiple directives [ngConfirmField, popover] asking for
new/isolated scope on: <input id="confirmPassword" name="confirmPassword" type="password"
ng-model="user.confirmPassword" placeholder="Confirm" popover="{{(autofields
.confirmPassword.$valid) ? 'This field is valid' : ((autofields.confirmPassword.$error
.required? 'This field is required' : '')+(autofields.confirmPassword.$error.minlength?
'This is under minimum length' : ''))}}" ng-confirm-field="" confirm-against="user
.password" required="required" ng-minlength="6" class="form-control" popover-trigger
="focus" popover-placement="top">
```

Changed the code to read directly from parent scope with `scope.$eval`. Tests pass.