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. 
What are your thoughts about this: We still perform the protocol check. But if the protocol is unrecognized, instead of preventing the addition of the link, we notify the user that the URI wasn't recognized by zotero and ask them to double-check their input. If they are satisfied with their input, simply add the link after they confirm. I think this would be a crude method to prevent misspelled URIs from entering the database. For example, if someone intended to enter a devonthink URI but accidentally typed x-devotnhink-item - they'd be alerted. 

Also if someone enters a protocol-less URI that we assume is a web address (for example, github.com) and we prepend http:// - we could alert the user of the change and ask for their conformation - that way, we don't change the user's input without their knowledge and/or consent. It could be that they don't want that. 

Finally, I've been working on making a custom window that would allow the user to specify a title in addition to the link. One idea I have is to enable a checkbox to the left of the address box with a value "http://" and by default the box is checked. However, as the user inputs text, if a protocol is detected in the input field, the box becomes unchecked. The status of the checkbox would enable/disable prepending the "http://" to the input. This process seems like a more upfront and transparent means of altering the input of a user.