add UpgradeSettings and ApplicationSettingsBase methods to interface
add UpgradeSettings and ApplicationSettingsBase methods to interface

- Added a UpgradeSettings property to IWindowPlacementSettings, which
defaults to true
- Added a `void Upgrade()` method to IWindowPlacementSettings, which is
implemeneted by ApplicationSettingsBase

xxMUROxx/MahApps.Metro,ye4241/MahApps.Metro,batzen/MahApps.Metro,p76984275/MahApps.Metro,chuuddo/MahApps.Metro,pfattisc/MahApps.Metro,psinl/MahApps.Metro,MahApps/MahApps.Metro,Danghor/MahApps.Metro,Jack109/MahApps.Metro,jumulr/MahApps.Metro,Evangelink/MahApps.Metro