metadataView: reactivate

[bwbohl]

There used to be a metadata view for both MEI and TEI files that would parse the header to a human-readable HTML page. Currently, this view is deactivated (commented out) in the code. I think nothing should be disabled by default in the code. If something needs to be hidden, there should be an injection point or a preference variable to control the behaviour or the feature should be deprecated.

[bwbohl]

Of course, the code might have to be updated and tested with some data. This might involve XSLT development.