Cleaning up Javadocs in core-ui classes.
Added common constants to AbstractCellFormatter.

Change-Id: Ie20ea62f059646e7d6c7f3660dd60a60c40532fe
diff --git a/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java b/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java
index d44836f..9966a88 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/cell/AppIdFormatter.java
@@ -24,6 +24,8 @@
  */
 public final class AppIdFormatter extends AbstractCellFormatter {
 
+    private static final String COLON = " : ";
+
     // non-instantiable
     private AppIdFormatter() { }
 
@@ -31,7 +33,7 @@
     @Override
     protected String nonNullFormat(Object value) {
         ApplicationId appId = (ApplicationId) value;
-        return appId.id() + " : " + appId.name();
+        return appId.id() + COLON + appId.name();
     }
 
     /**