Support ShortTitles for Multi Value Elements (introduced in IOS 5.0)

Added support for the ShortTitles key in Multi Value elements. 
Also added a usage example in the sample app.

for a description of this key, see: http://developer.apple.com/library/ios/#documentation/PreferenceSettings/Conceptual/SettingsApplicationSchemaReference/Articles/PSMultiValueSpecifier.html#//apple_ref/doc/uid/TP40007016-SW1