Xamarin.Forms 1.3.0.6284-pre3

## New API - Device.GetNamedSize (NamedSize size, Type targetType); Same as Device.GetnamedSize (NamedSize size, Element element) but doesn't require an instance. ## Bug Fixes ### Core - ListView/TableView respect WidthRequest/HeightRequest again (regression in 1.3.0-pre2) - No longer crash when trying to download/access the same UriImageSource on hundreds of images (System.IOException). - XAML now properly supports referencing other StaticResources from an Application subclass. - Fix issue where Grid sometimes measured out taller than it should, especially in ListView/StackLayout. Grid now prefers to expand in the direction of a "defined" constraint, which tends to match expected behavior when measuring. If both constraints are Infinite, previous behavior is retained. - BindableObject.SetValue will now properly perform loss-less conversions on base types. e.g. Calling slider.SetValue (Slider.ValueProperty, 6.0f) will now work correctly. - Fix issue where StackLayout in a Horizontal orientation would return an incorrect MinimumHeight in GetSizeRequest. ### iOS - ImageCell no longer flashes old image on cell re-use. - Slider now updates bindings correctly due to conversion fix. ### Android - Label.FontSize = 18 no longer accidentally gives a font size of 14 on any devices. - Fix another case where ScrollView content could flow outside of bounds (yay). - Fix crash in WebView when being removed from the visual tree. - Map no longer re-centers on Layout. ### WinPhone - Back button now closes ActionSheets and Alerts before attempting Navigation. - Picker no longer shows a bunch of blank entries. - ListView selection now properly shows up. - ListView allows selection of items multiple times in a row if the user calls SelectedItem = null. This behavior matches other platforms correctly now. - Label now reports the correct minimum width to match other platforms.