#4 extend source types

[Florian Sager]

Working on a rather new topic which is rather discussed
in industry than science, there are often no books and
no papers available.
Instead I have a bunch of multimedia files (Powerpoint,
online videos) which I will cite including a wwwlink.

The data model for WWWLinks has to be extended in my
view to be useful in this context:
- a file read/change-button would be useful to open a
copied www-file from a local drive (helpful if those
sources are published for a closed community and
therefore cannot be opened directly using the 'Link-view'
functionality).
- authors (and publishers) should be opt. addable to a
wwwlink
- a position field would be useful to write down the time
of a citation in a video stream or the relevant slides of a
powerpoint presentation
- two date fields 'last modified' and 'viewed on date' are
useful in the fast moving web.

Commonly said a WWWLink could become the same
status of the as the other sources (books, journals
a.s.o.).