Editor: allow adding and perhaps deleting media types for existing resources

[cspurk]

From Gunn Lyse (META-NORD, University of Bergen) in the META-SHARE support forum:

When creating a new metadata record, the first thing to do is to select ResourceType (e.g. corpus) and then to select the media types relevant for this corpus.

We have experienced 'the hard way' that it is extremely important to be dead sure that all relevant media types are selected before you priceed. Specifically an acoustic resource only got the media type Audio.

Unfortunately you cannot currently go back and add more media types at a later stage (e.g. adding the possibility to describe resource components belonging to the media type text).

In terms of user-friendliness, this missing technical facility is a serious drawback. (We had to create a dummy resource to describe the media type text, then paste this XML code into the XML of the original resource, which is obviously not a very user-friendly solution if less technically skilled persons are to use our editor).