Comment 6 for bug 1532611

Leading edge lives on "home/milanp/LP1532611_modular_format_V2"

Added some improvements and checks, based on comments from Britton Kerin. Improved code culture, fixed some bugs.
- added pre-selection of current/default format in save/load dialogs
- enforced the existence of at least on format which supports both load/save operations; the same applies for default format
- added more safety checks to avoid accidental data loss

Milan