Vienna 3.8.0 Beta 1

• Implement an experimental new browser based on WKWebView : it can be selected in Advanced preferences, and will be available after application restart. It is fastest and more secure.
• Refactor code:
  • modify ArticleController to be a NSViewController
  • structurate code around protocols like Browser, Tab, ArticleContentView, ArticleViewDelegate and BrowserContextMenuDelegate
  • change many methods of BaseView protocol to be optional and remove unneeded code
  • introduce new classes : ArticleConverter, ArticleStyleLoader, RSSSubscriber
• Remove preference setting related to notifications (already handled by System Preferences)
• Fix image overflow with certain feeds
• Fix scripts handling in menubar
• Fix behavior when clicking on Dock icon
• Update Sparkle to version 1.26
• Use NSFileManager properties for library paths
• Migrate some tests to Swift
• Update procedures for building binaries (don't use Bintray anymore, fix notarization)