NIHVIVO-3088 On error in Freemarker servlet processing, display stack trace to authorized users.

webapp/web/templates/freemarker/body/about.ftl

@@ -4,10 +4,10 @@
 
 <h2>${title}</h2>
 
-<#if aboutText??>
+<#if aboutText?has_content>
     <div class="pageGroupBody" id="aboutText">${aboutText}</div>
 </#if>
     
-<#if acknowledgeText??>
+<#if acknowledgeText?has_content>
     <div class="pageGroupBody" id="acknowledgementText">${acknowledgeText}</div> 
 </#if>

webapp/web/templates/freemarker/body/error/error-display.ftl

@@ -0,0 +1,23 @@
+<#-- $This file is distributed under the terms of the license in /doc/license.txt$ -->
+
+<#-- Template for general system error. -->
+
+<p>
+    There was an error in the system. 
+    <#-- This error has been reported to the site administrator. -->
+</p>  
+    
+<#if errorData??> <#-- view for site administrators -->
+   <#if errorData.errorMessage?has_content>
+        <p><strong>Error message:</strong> ${errorData.errorMessage}</p>
+    </#if>
+    <#if errorData.stackTrace?has_content>
+        <div>
+            <p><strong>Stack trace</strong> (full trace available in the vivo log):</p>
+            ${errorData.stackTrace}
+        </div>
+    </#if>    
+<#elseif ! urls.currentPage?ends_with("home")> <#-- view for other users -->
+    <p>Return to the <a href="${urls.home}">home page</a>.</p> 
+</#if>
+