Automatically find bit rate and bit depth when importing album

[sebastsg]

Currently the import UI is relying on file extensions, but there are two problems:

1. It won't find bit rate and bit depth
2. It's done manually during import - waste of time, and may result in errors

As part of this issue, it is a good opportunity to alter the "audio_format" table. Adding bit rate and bit depth as columns, and remove the now redundant "quality" column.