kcms/autostart: Show correct icons for scripts

Previously all autostart scripts were using the icon "dialog-scripts" Now scripts get their icon according to their file type python scripts have python logo and so on. But for the scripts that icon couldn't be determined, they use "dialog-scripts"

Now when adding a new login script, the correct icon for it's file type is added to desktop file. Therefore previously added autostart entries will still be using dialog-scrips icon. But for logout scripts though as they are saved as symlinks icon is determined when kcm is loaded.

Before

After (Had to remove all the login scripts and re-add them to change their icons)