Add Layout widget (#1041)

* Add width to panels
* Add height to panels
* Replace RenderContext with RenderOptions
* Remove exclusivity from alternative buffer
* Add Layout widget
* Add Align widget

src/Spectre.Console/IHasJustification.cs

@@ -0,0 +1,12 @@
+namespace Spectre.Console;
+
+/// <summary>
+/// Represents something that has justification.
+/// </summary>
+public interface IHasJustification
+{
+    /// <summary>
+    /// Gets or sets the justification.
+    /// </summary>
+    Justify? Justification { get; set; }
+}