1. add the option the code to be used under GPLv2 or GPLv3; previously only GPLv2 was allowed
2. add the "proxy option" as described in GPLv3 so we can add future licenses without having to bulk-edit everything again :)
3. remove the awkward "exception for MIT code in Mac client" clause; it was unnecessary and confusing.
When opening the "Add URL" dialog, check the clipboard selection & clipboard proper to see if either contains a URL, magnet link, or info hash code. If it has any of those things, put that in the dialog's entry field as the default action. Patch by cantabile.