Support URL schemes other than HTTP and HTTPS

[paulbartrum]

I've updated UniversalMarkdown to support the following URL schemes (the same list of URL schemes that reddit itself supports) in hyperlinks:

• FTP e.g. "ftp://test.com"
• STEAM e.g. "steam://test.com"
• IRC e.g. "irc://test.com"
• NEWS e.g. news://test.com
• MUMBLE e.g. "mumble://test.com"
• SSH e.g. "ssh://test.com"
• MAILTO e.g. "test@test.com"

These links generally work in Baconit, without any changes, but the app is left with an unsightly and useless forever-loading screen. It'd be nice to properly support these types of links.