Add single-file templates

[rolfbjarne]

We used to have a few templates to create single files:

• Empty xib (https://github.com/xamarin/vsmac-xamarin-extensions/blob/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/XIB/Empty.xft.xml)
• View - xib (https://github.com/xamarin/vsmac-xamarin-extensions/blob/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/XIB/View.xft.xml)
• CollectionViewCell: https://github.com/xamarin/vsmac-xamarin-extensions/tree/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/CollectionViewCell
• TableViewCell: https://github.com/xamarin/vsmac-xamarin-extensions/tree/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/TableViewCell
• Various SceneKit particle systems: https://github.com/xamarin/vsmac-xamarin-extensions/tree/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/SceneKit
• Various SpriteKit particle effects: https://github.com/xamarin/vsmac-xamarin-extensions/tree/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/SpriteKit
• Asset catalog: https://github.com/xamarin/vsmac-xamarin-extensions/blob/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/AssetCatalogEmpty.xft.xml
• Application manifest (Info.plist): https://github.com/xamarin/vsmac-xamarin-extensions/blob/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/IOSApplicationManifest.xft.xml
• Entitlements: https://github.com/xamarin/vsmac-xamarin-extensions/blob/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/IOSEntitlements.xft.xml
• LaunchScreen: https://github.com/xamarin/vsmac-xamarin-extensions/blob/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/LaunchScreen.xft.xml
• Settings bundle: https://github.com/xamarin/vsmac-xamarin-extensions/blob/47507384987d5522983bce0d92afb799b96b5a96/MonoDevelop.IPhone/MonoDevelop.IPhone/templates/Xamarin.iOS/File/SettingsBundle.xft.xml

We should look into porting some of these to .NET.