Improve track grouping view; add grouping collections

[GoogleCodeExporter]

Improve track grouping view; add grouping collections.

Screenshot 1 - Grouping in the Qmmp

Screenshot 2 - Grouping in the Foobar2000

Excerpts from the Foobar2000 manual
"%title% Title of the track. If “title” metadata field is missing, file 
name is used instead.

%artist% Name of the artist of the track. Checks following metadata fields, in 
this order: “artist”, “album artist”, “composer”, “performer”.

%album artist% Name of the artist of the album specified track belongs to. 
Checks following metadata fields, in this order: “album artist”, 
“artist”, “composer”, “performer”. The difference between this and 
%artist% is that %album artist% is intended for use where consistent value 
across entire album is needed even when per-track artists values vary.

%track artist% Name of the artist of the track; present only if %album artist% 
is different than %artist% for specific track. Intended for use together with 
%album artist%, to indicate track-specific artist info, e.g. ”%album artist% 
- %title%[ '//' %track artist%]” - in this case, last part will be displayed 
only when track-specific artist info is present."

Screenshot 1
http://itmag.es/48dck

Screenshot 2
http://itmag.es/5z3kB

Original issue reported on code.google.com by Dmk...@gmail.com on 12 Aug 2014 at 9:12