Added AvaloniaUI project.

Harmonia.UI/Views/PlaybackBar.axaml

@@ -0,0 +1,17 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:vm="clr-namespace:Harmonia.UI.ViewModels"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+			 DataContext="{x:Static vm:ViewModelLocator.PlaybackBarViewModel}"
+             x:Class="Harmonia.UI.Views.PlaybackBar"
+             x:DataType="vm:PlaybackBarViewModel">
+  <Design.DataContext>
+    <!-- This only sets the DataContext for the previewer in an IDE,
+         to set the actual DataContext for runtime, set the DataContext property in code (look at App.axaml.cs) -->
+    <vm:MainViewModel />
+  </Design.DataContext>
+
+  <TextBlock Text="{Binding Greeting}" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+</UserControl>