interface.py

+ points can be moved (mouse wheel)
+ added PCEN
+ added bspline
+ added modification of annotations after saving
+ access to saved data simplified
- removed legend to access categories
+ added listbox to access categories
- removed button to add categories
+ added shortcut to add categories one by one

~ replaced "classes.py" with "interface.py"
    |-> many changes (style + shortcuts + simplifications)
~ updated documentation and organisation
~ updated readme