Fixed error where Ginga cannot save preferences

	modified:   ginga/Control.py
	modified:   ginga/gtkw/GingaGtk.py
	modified:   ginga/qtw/GingaQt.py
	modified:   scripts/ginga

- Ginga now creates a $HOME/.ginga directory if it does not exist
- also removed deprecated calls to 'to_default_mode'