Clean up public API

* Make things a bit more consistent
* Add extension methods to configure things like tables, panels and grids.

src/Spectre.Console/Rendering/Traits/IHasBorder.cs

@@ -0,0 +1,25 @@
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Represents something that has a border.
+    /// </summary>
+    public interface IHasBorder
+    {
+        /// <summary>
+        /// Gets or sets a value indicating whether or not to use
+        /// a "safe" border on legacy consoles that might not be able
+        /// to render non-ASCII characters.
+        /// </summary>
+        bool SafeBorder { get; set; }
+
+        /// <summary>
+        /// Gets or sets the kind of border to use.
+        /// </summary>
+        public BorderKind Border { get; set; }
+
+        /// <summary>
+        /// Gets or sets the border color.
+        /// </summary>
+        public Color? BorderColor { get; set; }
+    }
+}