* Adds a "Tags" field to the post replacement dialog box. The given tags
are added to the post after replacement.
* Prefills the Tags field with certain tags that usually need to be
removed after replacement: replaceme, image_sample, jpeg_artifacts, etc.
* Record "file://#{filename}" as the replacement url when the
replacement comes from an uploaded file.
* Record the actual url downloaded by the upload process otherwise. This
may be different from the url given by the user, since the upload
process may rewrite the url.
Adds a "Final Source" field to the post replacement dialog. If
specified, the post's source field will be changed to this value after
replacement.
This makes fixing the source back to the HTML page after
replacement easier.
Bug: if a user replaces a post with another image, then replaces the
post back to the original image, then the deletion job for the original
image will still run. The will delete the original file, but that file
is now in use again and should not be deleted.
