Before this commit, it was not possible to upload again a file on the
browser from the composer, when it was added then removed from the attachments.
When a file is uploaded on the browser, it writes on a special input
some data to identify this file. In order to detect a new upload,
the code listens on the JQuery event `change` on this input. Since the
value of this input was not cleared after an attachment removal, the
user couldn't reupload the same file, because the value of the input
will be unchanged.
This commit solves this issue by clearing the special input when removing
an attachment, so that adding the same file again will trigger a `change`
on this input.
Alexandre Kühn
212ed85ac4