Link URI re: issue 486

The proposed changes address the silent failing of adding a link to an unrecognized URI. They allow the user to correct any potential mistakes made to the initial address through a prompt dialogue. 
We should do a better job at generating names (I know this is coming from the current implementation). Particularly, if this is a URL, then I think we want to display the host and not the file (and certainly not the parameters or the fragment). For everything else, I would just display the full URI, since I think the protocol would be very informative and there may or may not be useful information in the rest of the URI. The instance that I can think of where file name would be a good choice is `file:` URI, which we specifically disallow.