Fix the visibility converter

Yeah, this is silly... the CountToVisibilityConverter had its logic
backwards because it was being used to show textblocks with "XXX
required" messages in the publish control if those fields were not
filled out... which is why we have PromptTextBox controls to use!

Fix silliness.

Author: shana

src/GitHub.UI/Converters/CountToVisibilityConverter.cs

@@ -15,7 +15,7 @@ public class CountToVisibilityConverter : ValueConverterMarkupExtension<CountToV
     {
         public override object Convert(object value, Type targetType, [AllowNull] object parameter, [AllowNull] CultureInfo culture)
         {
-            return ((int)value == 0) ? Visibility.Visible : Visibility.Collapsed;
+            return ((int)value > 0) ? Visibility.Visible : Visibility.Collapsed;
         }
     }
 }

src/GitHub.VisualStudio/UI/Views/Controls/RepositoryPublishControl.xaml

@@ -94,36 +94,26 @@
     </ComboBox>
 
     <Grid>
-      <TextBox x:Name="nameText"
+      <ui:PromptTextBox x:Name="nameText"
                Height="23"
                Margin="0"
                Background="{DynamicResource GitHubVsSearchBoxBackground}"
                Foreground="{DynamicResource GitHubVsWindowText}"
                MaxLength="{x:Static cache:Constants.MaxRepositoryNameLength}"
-               Text="{Binding RepositoryName}" />
-
-      <TextBlock Margin="7,4,0,0"
-                 Foreground="{DynamicResource GitHubVsGrayText}"
-                 IsHitTestVisible="False"
-                 Text="{x:Static prop:Resources.RepoNameText}"
-                 Visibility="{Binding ElementName=nameText, Path=Text.Length, Converter={ui:CountToVisibilityConverter}}" />
+               Text="{Binding RepositoryName}"
+               PromptText="{x:Static prop:Resources.RepoNameText}" />
     </Grid>
 
     <Grid>
-      <TextBox x:Name="description"
+      <ui:PromptTextBox x:Name="description"
                Height="52"
                Margin="0,8,0,0"
                AcceptsReturn="True"
                Background="{DynamicResource GitHubVsSearchBoxBackground}"
                Foreground="{DynamicResource GitHubVsWindowText}"
                Text="{Binding Description}"
-               TextWrapping="WrapWithOverflow" />
-
-      <TextBlock Margin="7,12,0,0"
-                 Foreground="{DynamicResource GitHubVsGrayText}"
-                 IsHitTestVisible="False"
-                 Text="{x:Static prop:Resources.DescriptionOptional}"
-                 Visibility="{Binding ElementName=description, Path=Text.Length, Converter={ui:CountToVisibilityConverter}}" />
+               TextWrapping="WrapWithOverflow"
+               PromptText="{x:Static prop:Resources.DescriptionOptional}" />
     </Grid>
 
     <CheckBox x:Name="makePrivate"