ability for collection scanning to recover from errors when reading a file

When starting Groove Basin it scans your music folder to build the music collection.
Problem: after startup is complete (and lots of messages about "max_analyze_duration 5000000 reached" and "Estimating duration from bitrate, this may be inaccurate"), my collection is missing a lot of songs.
Probable cause:

```
library scanning error: Error: ENOENT, lstat '[...]/Classical/Maurice André/Albinoni - Concerto � cinque r� majeur 1.mp3'
```

Ok, this filename seems to be badly encoded but it seems the scanning process is aborting on the first error it encounters.
A better solution would be to skip invalid entries and log them altogether at the end of the scanning process. All the problematic files would be logged in the same "log paragraph" (not scattered between warnings and such) and would be easily spotted by the user.