improve session

It would be nice to have at least a session for debugging and editing, as requirements may differ slightly depending on the active task.

During editing I'd like to have the editor splitted to show multiple files, where as during debugging, I'd like to have only one editor - so it would be nice, if session handling could silently unsplit the editors for debugging and restore the splitted state (with active files) on ending debug session.

Additionally I'd like to have the session save more states, like the width and order of columns in local variables-, stack- and breakpoint-tables.

Furthermore it would be nice, if the session could save the expand-state of local variables, so if you switch to other stacklevels and come back, the expanded variables will be expanded as before.