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. 
I believe it is still in the code - its just been moved down a few lines as a result of the additional code. It should be on [line 3056] (https://github.com/mtd91429/zotero/blob/linkURI/chrome/content/zotero/zoteroPane.js#L3056). I also really like the trim() idea - that is something I hadn't considered.