Threaded batch mode

[sezanzeb]

• threaded conversion in batch mode
• reduced number of prints with -q
• -t option: when -q is provided don't print nothing at all, rather just hide errors and files without tags
  because otherwise the combination of -t and -q makes no sense at all
• removed info about which gtk version is used and such. Not relevant to the user
• fixed an error from one of my recent commits
• added -c mode, doing what the gtk interface does when loading files. showing which ones cannot
  be converted.
• the CliProgress class accepts multiple arguments like print to create messages now:
  show("a", "b")
• nicer console output

example output of -b (-q disables all output):

SoundConverter 3.0.1

checking files and walking dirs in the specified paths...
Queue start: 36 tasks, 4 thread(s).
Queue done in 0.052s (36 tasks)

preparing converters...
overwriting '/funky_files/converted/original/audio 2.ogg'
skipping 'not_music.ogg': invalid soundfile
skipping 'not_music.flac': invalid soundfile
(...)
overwriting '/funky_files/converted/original/foo/audio 4.ogg'
overwriting '/funky_files/converted/original/foo/bar/audio 5.ogg'
overwriting '/funky_files/converted/original/foo/bar/audio 6.ogg'

starting conversion...
Queue start: 6 tasks, 4 thread(s).
1/6: '/funky_files/original/audio 2.flac'
2/6: '/funky_files/original/audio 1.flac'
3/6: '/funky_files/original/foo/audio 3.flac'
4/6: '/funky_files/original/foo/audio 4.flac'
5/6: '/funky_files/original/foo/bar/audio 5.flac'
6/6: '/funky_files/original/foo/bar/audio 6.opus'
Queue done in 12.346s (6 tasks)

example output of -c (-q just prints a naked list of file paths):

SoundConverter 3.0.1
Queue start: 36 tasks, 4 thread(s).
Queue done in 0.052s (36 tasks)

Non-Audio Files:
/funky_files/original/not_music.ogg
/funky_files/original/not_music.flac
(...)
/funky_files/original/pictures/pic (another copy).jpg

[sezanzeb]

after this PR the last thing I want to implement in batch mode is instead of overwriting, adding a (1), (2), .. suffix, just like the gtk tool. But that has low priority for me, idk when I will do that

[sezanzeb]

And I'll write a test for prepare_files_list later

[kassoulet]

Great, thanks!