Support URL Scheme to open apps in web browsing mode

[ryh]

tl;dr:
add an option to open URL Scheme to open apps.
OR just respect the setting "openExternalLinksInBrowser"
OR a whitelist allowing users to specify trusted schemes.

FULL version
I use webpages in Plash as dynamic wallpaper , was wondering open app with URL Scheme like vscode://, maps://, x-xcode-documentation:// (open xcode documents) would be fun, but on the other hand, worrying about web may abuse the URL Scheme to harm users, please give feedback, thanks.
I did add one line to handle this feature in local build, it won't break sandbox, and WebViewController did warn about first open, but only one time for all scheme.