[IZPACK-1081] - Summarize UserInputPanel Feature

This is to address feature request http://jira.codehaus.org/browse/IZPACK-1081

To get the header/caption and/or fields of the UserInputPanel summarized, use the "summaryKey" attribute in the userInputPanelSpec.xml file. If not specified the UserInputPanel will not be summarized. 

Note: You must summarize the header/caption if you want to summarize a field of the UserInputPanel.

Ex.
```
		<panel id="example.panel" summaryKey="caption.string.key">
		    <field type="title" bold="true" size="2" id="example.panel.title"/>
		    <field type="staticText" id="exmple.panel.info"/>
		    <field type="space"/>
		    <field type="text" variable="example.user" summaryKey="label.string.key">
		       <spec id="example.user" size="16" />
		    </field>
		    <field type="space"/>
		    <field type="password" variable="example.password">
		        <spec>
		            <pwd id="example.password" size="16" />
		            <pwd id="example.password.confirm" size="16" />
		        </spec>
		    </field>
		</panel>
```