[TIMOB-18743] Windows: Implement Ti.UI.ListView.searchText property for filtering

Setting a ListView's searchText property does nothing right now. It should filter the items based on the search text. Unfortunately Windows doesn't make this easy for us. Looks like we need to filter the collections ourselves under the hood: - http://docs.appcelerator.com/titanium/3.0/#!/api/Titanium.UI.ListView-property-searchText - http://stackoverflow.com/questions/11642528/windows-metro-app-filtering-listview-and-showing-specific-data-from-list - http://stackoverflow.com/questions/14956999/filtering-and-sorting-of-an-observablecollection-in-listview-binding - http://www.codeproject.com/Articles/527686/A-WinRT-CollectionView-class-with-Filtering-and-So