loading动画建议增加进度展示

[HaHa-ZYK]

当前loading动画无法提供进度的显示，在执行较长时间的操作时用户无法感知当前命令的执行情况，无法判断操作是否正常执行，建议在目前的基础上增加进度展示。
增加设置进度的方法，传入0-1的百分比或最小值、最大值与当前值；
根据百分比设置加载弧形的角度，当为0%时仅显示1个点，当为100%时显示圆环。

[yanjinhuagood]

example

<CheckBox
    Name="MyCheckBox"
    HorizontalAlignment="Center"
    VerticalAlignment="Center"
    Checked="MyCheckBox_Checked"
    Content="StartLoading "
    Unchecked="MyCheckBox_Unchecked" />
<Button
    x:Name="BtnProgress"
    Width="50"
    HorizontalAlignment="Center"
    VerticalAlignment="Top"
    wd:ElementHelper.IsRound="True"
    Content="Progress" />

private DispatcherTimer _timer = new DispatcherTimer();
private int _currentProgress = 3;
private DispatcherTimer _timer = new DispatcherTimer();
private int _currentProgress = 3;
public LoadingExample()
{
    InitializeComponent();
    Loaded += OnLoadingExample_Loaded;
}

private void OnLoadingExample_Loaded(object sender, RoutedEventArgs e)
{
    _timer.Interval = TimeSpan.FromMilliseconds(500);
    _timer.Tick += (s, args) =>
    {
        if (_currentProgress <= 100)
            _currentProgress += 3;
        else
            _timer.Stop();
        Loading.SetValue(BtnProgress, _currentProgress);
    };
}
private void MyCheckBox_Checked(object sender, RoutedEventArgs e)
{
    Loading.SetLoadingType(BtnProgress, LoadingType.Progress);
    Loading.SetValue(BtnProgress, _currentProgress);
    Loading.SetIsShow(BtnProgress, true);
    _timer.Start();
}
private void MyCheckBox_Unchecked(object sender, RoutedEventArgs e)
{
    _currentProgress = 0;
    Loading.SetIsShow(BtnProgress, false);
    _timer.Stop();
}