Many changes to attachLink window:
  - converted from window class to dialog class
  - localized strings
  - returned input to caller function addAttachmentFromURI in zoteroPane.js
    prior to submitting to linkFromURL function in attachments.js
  - fixed indentation issues

TODO:
[] work on linkFromURL function in attachments.js to ensure input is sent to
   cleanAttachmentURI function in case linkFromURL is called by a translator
[] modify automatic title generation function for linked URIs (maybe?)
[] move title textbox to top in dialog prompt (maybe?)