Arrange member groups depending on their availability rework

#### Purpose

Rework PR https://github.com/Benglin/Dynamo/pull/36 according the comment https://github.com/Benglin/Dynamo/pull/36#issuecomment-54774092.

#### Modifications

1. TextBlocks are created in XAML.
2. TextBlock's `Visibility`, `Text`, `FontWeight` properties are bound in XAML.
3. Converters created for `Text` and `FontWeight` properties.
4. Switching between styles is done in converter.

#### Additional references

[Link](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4521) to YouTrack task.

#### Reviewers

@aosyatnik, please take a look. 
The above three properties cannot be settable, we will never need to set their values. They should be implemented like below:

```cs
public bool IsPrimaryHeaderVisible
{
    get
    {
        // If there are class members, display the primary header.
        var info = this.DataContext as ClassInformation;
        return ((info == null) ? false : info.CreateMembers.Any());
    }
}
```

Also, rename ```PrimaryHeaderVisibility``` to ```IsPrimaryHeaderVisible``` (same for all three).