new class for managing midvatten settings
	modified:   customplot.py
	modified:   definitions/midvatten_defs.py
	modified:   midvatten.py
	modified:   midvatten_utils.py
	modified:   midvsettings.py
	renamed:    midvsettings.py -> midvsettingsdialog.py
	modified:   ui/customplotdialog.ui