Replace use of deprecated -[NSOpenPanel beginSheetForDirectory:...].

However, as long as we're still deploying to 10.6, we can't use this because eour undocumented use of -[NSOpenPanel setDirectoryURL:] to set a file URL doesn't work properly on 10.6.  It does on 10.7, 10.8 and presumably 10.9.
Update copyright date in LICENSE.
Partially update Read Me for 1.1.

Retina screenshots, etc.