Split into two panes, source editor and text editor

[timbl]

The problem here is that when we are talking about a data file like, say, a meeting definition file, then this view is one only developers should get as an option as “Source view” of the data. When it is a plain text file, then a normal user should get it as the the default view of a plain text note file, so not “Source” or maybe “Text” or “View/edit” or something should be the pane name. So really it should be two panes, with different priorities and different targets and different icons and different labels.