Better background handling in themes

- Modify view structures so that we're able to
  control background drawing better
- Remove transparent concept from box view
- Add background styles for dialog, menu/status bars
- Relates #824

spring-shell-samples/spring-shell-sample-catalog/src/main/java/org/springframework/shell/samples/catalog/Catalog.java

@@ -245,11 +245,19 @@ public class Catalog {
 		}
 
 		@Override
-		public void draw(Screen screen) {
+		protected void drawBackground(Screen screen) {
+			int bgColor = resolveThemeBackground(getBackgroundStyle(), getBackgroundColor(), -1);
+			if (bgColor > -1) {
+				Rectangle rect = getRect();
+				screen.writerBuilder().build().background(rect, bgColor);
+			}
+		}
+
+		@Override
+		protected void drawContent(Screen screen) {
 			Rectangle rect = getRect();
 			Writer writer = screen.writerBuilder().style(getStyle()).build();
 			writer.text(String.format("%-20s %s", getItem().name(), getItem().description()), rect.x(), rect.y());
-			writer.background(rect, getBackgroundColor());
 		}
 	}
 

spring-shell-samples/spring-shell-sample-catalog/src/main/java/org/springframework/shell/samples/catalog/CatalogConfiguration.java

@@ -59,6 +59,26 @@ class CatalogConfiguration {
 			return "bg:blue";
 		}
 
+		@Override
+		public String dialogBackground() {
+			return "bg:green";
+		}
+
+		@Override
+		public String buttonBackground() {
+			return "bg:red";
+		}
+
+		@Override
+		public String menubarBackground() {
+			return "bg:magenta";
+		}
+
+		@Override
+		public String statusbarBackground() {
+			return "bg:cyan";
+		}
+
 	}
 
 }