show layout source file and line number in tooltip in preferences
fix performances problems with autoupdated lists

The recently added autoupdate mode lacked optimizations for many consecutive changes,
and didn't check hard enough if a re-sort was really needed
improve code for multi-value BuildChoiceMenu
move code from artist regex options to a generic NewPrefMultiCombo function
add "Ignored file extensions" option

remove "Do not add songs that can't be played" option
move code that adds filechooser filters to a common function
hide non-music files from "add files or folders" dialog
change arguments of ChooseDir() function
don't print messages in normal operation, add -verbose option

playing/scanning messages on stderr are now only printed with -verbose
-debug option implies -verbose option