Enable moving note/group
When right clicking a group or a note, the context menu now has a new entry: 'Move'.
This action let's the user choose where the selected element will be moved. If a note is selected, let the user choose between group and category; if a group is selected, the user will only be able to choose category, since a group can't be inside a group.
Moving the item will move it both visually on the Treeview but also on the system itself.