in attachLink.js
  - expanded submit function to clean the link entered and attach to the item
  - expanded submit function to prevent attaching link to file and displaying an alternate message to the user
  - expanded submit function to alert user of an unrecognized uri

in attachLink.xul
  - defined global key short cuts for submit (return key) and cancel (escape key)
  - defined multiple messages to be displayed depending on the user input
  - tied messages to zotero.dtd file

in attachments.js (ported from branch linkURI commit 55bc0ca)
  - in function cleanAttachmentURI, removed regex filters and utilized nsIIOService for screening
  - in function linkFromURL, removed regex filter
  - in function linkFromURL, altered title generation function to prevent it from generating a blank title if the last character in the string is '/'

in zoteroPane.js
  - in addAttachmentFromURI, removed the commented-out nsIPromptService code that was left over from the fork
  - in addAttachmentFromURI, made the window resizable

in zotero.dtd
  - added entities for the attachLink window

TODO:
[ ] tweak overall window design (e.g. size, button positioning, textbox width, etc.)
[ ] correct window flex when an alternate message is displayed (window doesn't currently expand to display all visible content)
[ ] automatically submit file links to the linkFromFile function instead of displaying an error?