duration field for video-links

[Wolfgang Thomas]

Hi,

I have a video container that contains Files (IVideoEnhanced) and Links
(IVideoLinkEnhanced). The video-container.html provides a nice formatting.

Beneath each video's image, "Time:" is displayed. I can set a value for
it in the "duration" field of enhanced File objects; but this field is
not available for enhanced Link objects.

Imho it is sufficient to
- add a duration field inside the VideoLinkEditForm
(videoifaces.IVideo['duration'])
- and to provide a method duration(self) in the VideoLinkView
(both in p4a.plonevideoembed.browser).

Plus add the duration display to video-link.pt

If I do this, I get the duration field on the edit-form; and its value
is then displayed on the video-container view. And the
p4a.plonevideoembed tests don't break :)

I'd like to commit these changes, any objections?

An alternative could be to make showing the duration conditional in
video-listed-single.pt.

Cheers,
Wolfgang