TODO

[x] menubar (fring,help)
    [x] refresh
    [x] save to file
    [x] select directory
    [x] show hidden files
    [x] "about" dialogue
    [x] open parent folder

[x] click on folder -> open it
[x] show busy cursor while walking dir tree

[ ] always render text on top
[ ] make sure that filenames are always visible
[ ] do more magic adjustments
[ ] clean gui -> renderer interface
[ ] do not show black backrgound when app starts up