It closes #2349.

It simplify the flac decoder code.
It fixes the build of the packetizer when flac is disabled.
It makes the flac packetizer behaviour independant of the flac decoder presence.

Signed-off-by: Pierre d'Herbemont <pdherbemont@free.fr>

- keep root index of views when searching
- clear search when browsing or changing view
- layout and geometry fine tuning

Performs much better.
URL is sanitized by filename_sanitize() just as title before.

We may be joining the input_thread inside the vlm lock, and try to vlm lock inside the stop event handler.

prefer more uri-friendly file://dir_path to dir://dir_path

this also solves uri alteration on Windows (recent regression)