TEIIDDES-2548: Handling NUL character in SQL String

* The NUL character can added to an ESCAPE clause using its unicode
  counterpart \u0000 and this is converted by java into \0. This character
  is problematic for printing in any display since printing will terminate
  at the first occurence of NUL.

* Using the SQL editor, users can enter the unicode string into the UI but
  on saving this is converted to \0. The DisplayNode tree still contains
  all nodes after the \0 but printing DisplayNode.toString() terminates too
  soon.

* TextDisplayNode
 * Protect the UI in the text from the \0 by returning \\u0000 (escaped
   version). This will display \u0000 in the UI and save it to the XMI file
   ensuring it can be safely deployed to Teiid.

plugins/org.teiid.designer.query.ui/src/org/teiid/query/ui/sqleditor/component/TextDisplayNode.java

@@ -7,6 +7,7 @@
  */
 package org.teiid.query.ui.sqleditor.component;
 
+
 /**
  * The <code>TextDisplayNode</code> class is used to represent text display nodes.
  *
@@ -57,7 +58,13 @@ public int setStartIndex(int index) {
      */
     @Override
     public String toDisplayString() {
-        return (isVisible() ? this.textStr : BLANK);
+        if (! isVisible())
+            return BLANK;
+
+        if (textStr.equals("\u0000")) //$NON-NLS-1$
+            return "\\u0000"; //$NON-NLS-1$
+
+        return this.textStr;
     }
 
     /**