RFC: Get rid of "overwrite" property in GrlData

["Juan A." Suárez Romero <jasuarez igalia com>]

Hello.

I explain here a proposal about removing the "overwrite" property in
GrlData.

This property was introduced so users could protect the current data in
a media to avoid plugins to overwrite it.

So users wanted to avoid overwritten current metadata in a GrlData,
could set that property to TRUE, so any attempt to overwrite the
metadata (specially from plugins) was futile.

Nowadays I don't see it so important, and to be honest I think nobody is
using it. If someone would be interested in this feature, I'm pretty
sure there are other ways to do it (like not asking for keys that
already have a value).

But what motivates this request is that, with the current multi-valued
approach, this property is completely broken.

What means the property in the context of multivalued elements? Can we
add new elements? Can we replace a single key from a related set of
keys? Can we delete a key?

Right now, the overwrite property is completely ignored when handling
multi-valued elements. And I see that very confusing.

In order to make things simpler, and also guessing nobody is using that
property, my suggestion is just to get rid of it. I would feel more
comfortable without it, as it would make clearer the GrlData.

As usual, opinions are welcomed.

	J.A.