Introduce "More" button for StandardPanel

#### Purpose

Add "More" button to StandardPanel as specified in [UI Proposal](https://docs.google.com/document/d/1sPlXdh2vsxU7gVbW-iKm1s1JtGYNh9hnvbD8L7wiAww). Design with button is presented below.
![sp more btn](https://cloud.githubusercontent.com/assets/8158551/4247077/ef0e88c8-3a54-11e4-9531-45f24ee3bd22.PNG)

#### Modifications

Add "More" button to `LibraryView.xaml`. Introduced `IsMoreButtonVisible` for controlling `Visibility` property. Also added two methods `ShowMoreButton()` and `HideMoreButton()`.

#### Reviewers

@Benglin, please review.
The more I think about this property, the more I feel it should not belong here in ```ClassInformation```, and you're right, we might need another layer called ```StandardPanelViewModel``` that takes care of filtering for the underlying ```ClassInformation``` object (we need ```ClassInformation``` object to serve as the ```Model``` layer and it returns only the ```data + icon```, and nothing else). Take note when you implement ```StandardPanelViewModel```, we should have a read-write property called ```bool ShowExtendedMembers``` on it.

Then when ```ShowExtendedMembers``` is ```false``` (by default), ```ActionMembers``` returns only the partial list, for example (the same can be applied to ```QueryMembers``` too):

```cs
// This is on ```StandardPanelViewModel``` level.
private List<BrowserInternalElement> actionMembers;
public IEnumerable<BrowserInternalElement> ActionMembers
{
    get
    {
        if (this.ShowExtendedMembers)
            return this.actionMembers;

        // Filter extended members for partial display.
        return this.actionMembers.Take(TruncatedMembersCount);
    }
}
```

I think we should take that as a separate PR, I will create a new task and add it to the main ```Conversation``` of this PR.