Improve the project directory window

[ignutanz]

• Autoscrolling feature to enable the scrolling of the window vertically based on the mouse move
• when clicking on a subdirectory in project directory, i have to use the scrollbar again to see the files if it was not already in the visible. Autoscroll to the clicked subdirectory area in this case.
• consider closing an open sub-directory when another subdirectory is clicked to be opened