Add in the ability to make custom overrides.

Fixed issues with the CSS in the property inspector
Make it so i can actually write unit tests if i want to

src/FocusVolumeControl/AudioSessions/ActiveAudioSessionWrapper.cs

@@ -10,9 +10,11 @@ using FocusVolumeControl.AudioSession;
 
 namespace FocusVolumeControl.AudioSessions;
 
+#nullable enable
+
 public sealed class ActiveAudioSessionWrapper : IAudioSession
 {
-	public string DisplayName { get; set; }
+	public string DisplayName { get; set; } = null!;
 	private List<IAudioSessionControl2> Sessions { get; } = new List<IAudioSessionControl2>();
 	private IEnumerable<ISimpleAudioVolume> Volume => Sessions.Cast<ISimpleAudioVolume>();
 
@@ -102,3 +104,4 @@ public sealed class ActiveAudioSessionWrapper : IAudioSession
 		return VolumeHelpers.GetVolumePercentage(level);
 	}
 }
+#nullable restore

src/FocusVolumeControl/AudioSessions/IconWrapper.cs

@@ -4,6 +4,8 @@ using FocusVolumeControl.UI;
 using System;
 using System.Drawing;
 
+#nullable enable
+
 namespace FocusVolumeControl.AudioSession
 {
 	public abstract class IconWrapper
@@ -101,3 +103,4 @@ namespace FocusVolumeControl.AudioSession
 	}
 
 }
+#nullable restore