Prevent user input via keyboard

This commit prevents the user from entering something into the text
field as this could currently lead to an exception

Change-Id: I30cb8c0846c93a82119cfb54dc6e2fe76df23d4c
diff --git a/org.eclipse.example.calc/src/org/eclipse/example/calc/internal/ui/swt/CalculatorUI.java b/org.eclipse.example.calc/src/org/eclipse/example/calc/internal/ui/swt/CalculatorUI.java
index 2961499..c943519 100644
--- a/org.eclipse.example.calc/src/org/eclipse/example/calc/internal/ui/swt/CalculatorUI.java
+++ b/org.eclipse.example.calc/src/org/eclipse/example/calc/internal/ui/swt/CalculatorUI.java
@@ -82,6 +82,8 @@
 		display = new Text(shell, SWT.BORDER_SOLID | SWT.RIGHT);

 		display.setLayoutData(gridData);

 		display.setText("0");

+		display.setEditable(false);

+		display.setBackground(Display.getCurrent().getSystemColor(SWT.COLOR_WHITE));

 		calculator.setClearText(true);

 	}