Fix multiselect population (Issue #333)

I've added demo on multiselect page with buttons that populate multiselect with values.
Model formatter was changed to accept inputValues not only 'as' value, but the whole object. For example in this case:

    <ui-select multiple ng-model="multipleDemo.populateSelection"...
       <ui-select-choices repeat="person.email as person in people...

According to old logic, we must populate multipleDemo.populateSelection with emails:

    multipleDemo.populateSelection = ["ex@example.com"];

Now we can do it like this:

    multipleDemo.populateSelection = [{name: 'Adam', email: 'adam@email.com', age: 12, country: 'United States' }];

So, if we get it from the backend, we need not to repopulate our model with "correct" values.
Also I've added correct object comparison there.

[Here](http://plnkr.co/edit/vL9L2XWeziTPuX4KxwmP?p=preview) is plunker from Issue #333. And [this](http://plnkr.co/edit/WbjwcT0UURmTEmOzgsFo?p=preview) is forker version with fixed select.js