Enable configuration of relative panel width

Some panels are regarded less important than others by stakeholders/ users. E.g. Metadata panel doesn't need as much relative width as the Text panel, especially as the transcript tab needs to show the full lines without additional linebreaks to stay true to the manuscript. Being able to configure the relative width in a config file would be nice to have. E.g. "Manuscript = 25%; Text = 30%; Commentary = 25%; Metadata = 20%