Show cover art box by default.

Average user is expecting cover art to be shown in such application.
Download cover art by default, one front image only.

Average user is expecting cover art to be shown in such application.
Set default size for CAA images to 500px.
All providers are enabled so the behavior is the same than MusicBrainz website
(which shows cover art from (ie.) Amazon by default).
For CAA, download only approved images by default.
Set preferred releases to "Digital Media" and "[Worldwide]" by default.

If two releases with same tracklist exists, we want to take digital media over CD (ie),
because most users are tagging digital files from unknown source and don't care
which exact release it is until tracklist is matching.

Worldwide is preferred by default, because if two releases exist with same tracklist
it is more likely it is the worldwide one's than a country-specific one.
Remove user info from logged urls

It is a safety measure as users may publish their logs ie. in bug reports.
Merge pull request #215 from zas/safelog

Remove user info from logged urls
Merge pull request #213 from zas/defaults

Attempt to provide better defaults for the average user
Use getopt.gnu_getopt

If you were ever annoyed by starting Picard from the console with a
specific folder, noticing you forgot the `-d`, stopping Picard, pressing
arrow-up, adding the `-d` to the end of the line, only to notice that
this didn't help at all, this commit is for you because now the option
parsing doesn't stop after the first thing that's not an option.
Merge branch 'master' of github.com:musicbrainz/picard
Add a missing `re` import

This is used by the code checking whether to ignore a to-be-loaded
directory.
Revert "Set preferred releases to "Digital Media" and "[Worldwide]" by default."

This reverts commit 2886d102a3149778ffbee739a1d73f90725130c0.

See comments at https://github.com/musicbrainz/picard/commit/2886d102a3149778ffbee739a1d73f90725130c0