Remove old/* plugins.

It's been almost 3 years since they were moved to the old/ folder, and
apparently they've not been needed enough by anyone to get an update
to current plugin API. If ever they're deemed useful again, they can
be pulled back via Git and updated.
Remove `open_in_gui.py` plugin.

The functionality is included in Picard's core now, so there is no
need for a plugin to do it as well.
Strip CR as well as LF to avoid errors on Windows
Merge pull request #255 from Freso/cleanup-contrib-plugins

Clean up contrib plugins
Use Universal Newline Support instead.
Merge pull request #257 from Sophist-UK/sophist_fix_test_bytes2human

Fix test bytes2human on Windows
Add `update_attributes` command to setup.py

It retrieves attributes.pot file from transifex and uses it to generate a python
file containing cover art types.

Generated file is picard/attributes.py
Add generated picard/attributes.py
Add po/attributes/attributes.pot to git ignore list

It doesn't have to be handled by picard translators.
Add 'musicbrainz.attributes' section to transifex config
Use `MB_ATTRIBUTES` generated list to build CAA_TYPES

`unknown` type is a special case, as it doesn't come from attributes.pot
Load attributes translations, hack is required to handle msgctxt ...

Without the msgctxt hack, strings aren't translated.
Basically search key has to be "context\x04message" instead of "message".

See http://bugs.python.org/issue2504
Translate cover art types in Options

You need to update translations for this to work, ie for local testing:
```
$> python setup.py get_po_files
$> python setup.pu build_locales -i
$> python tagger.py -d
```
Extend to apply to medium formats too.
Remove unneeded sort.
Extract release group primary and secondary types too.

This is not used yet as a modification of UI is needed, sliders are somehow hardcoded.
See https://github.com/musicbrainz/picard/blob/master/picard/ui/options/releases.py#L51
Merge `update_countries` and `update_attributes` in one command, `update_constants`