Clean up Widgets

* Move /Widgets/Live/* to /Live/*
* Move /Widgets/Prompt/* to /Prompts/*
* Move tests and expectations to match the new locations

src/Spectre.Console/Live/Progress/ProgressRenderer.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using Spectre.Console.Rendering;
+
+namespace Spectre.Console
+{
+    internal abstract class ProgressRenderer : IRenderHook
+    {
+        public abstract TimeSpan RefreshRate { get; }
+
+        public virtual void Started()
+        {
+        }
+
+        public virtual void Completed(bool clear)
+        {
+        }
+
+        public abstract void Update(ProgressContext context);
+        public abstract IEnumerable<IRenderable> Process(RenderContext context, IEnumerable<IRenderable> renderables);
+    }
+}