Fix issue with date format yyyy-mm

MB sometimes gives dates in form yyyy-mm. Mutagen cannot save id3v23
dates in this format and truncates them to yyyy. Then they don't match
when the file is reloaded.

This fix detects New metadata dates in this format and truncates them.
Fix stupid coding error in mimeo comment response.
Add 'Audio' to the categories in the .desktop file

As per
http://blogs.gnome.org/hughsie/2013/09/03/broken-desktop-files/
it should have both 'AudioVideo' and one or both of 'Audio' or 'Video'
in order to be categorized correctly.
Merge pull request #157 from kepstin/desktop-fix

Add 'Audio' to the categories in the .desktop file
Rename internal trackid to recordingid, add a new tag for trackids.
Fix the track test to include track mbid, change internal recording id name
Fix plugin install code

Fix following errors:

1. On plugin install:
Traceback (most recent call last):
File ".\picard\ui\options\plugins.py", line 133, in open_plugins
self.install_plugin(path)
File ".\picard\ui\options\plugins.py", line 138, in install_plugin
dest = os.path.join(self.tagger.user_plugin_dir, file)
AttributeError: 'Tagger' object has no attribute 'user_plugin_dir'

2. On Open Plugin Folder:
Traceback (most recent call last):
File ".\picard\ui\options\plugins.py", line 151, in open_plugin_dir
QtGui.QDesktopServices.openUrl(QtCore.QUrl(self.loader %
self.tagger.user_plugin_dir, QtCore.QUrl.TolerantMode))
AttributeError: 'Tagger' object has no attribute 'user_plugin_dir'.

Code missed from commit 7c4fdf765cd404ba0742f2513d039a5b69e8a71d on
2013-06-08.
Fix error when installing over existing plugins

As reported in PICARD-444, the following error is received when
installing over an existing plugin:

Traceback (most recent call last):
File ".\picard\ui\options\plugins.py", line 134, in open_plugins
self.install_plugin(path)
File ".\picard\ui\options\plugins.py", line 148, in install_plugin
self.tagger.pluginmanager.install_plugin(path, dest)
File ".\picard\plugin.py", line 198, in install_plugin
same_file = os.path.samefile(path, dest) if dest_exists else False
AttributeError: 'module' object has no attribute 'samefile'
Add explanatory comment
Add News.
Add recordingtitle as per PICARD-515

This fix adds a %_recordingtitle% script variable for use in renaming as
per PICARD-515.
Add News.
mbxml: move a comment to the code it refers to
Add releasetrackid to NEWS.txt
Merge branch 'sophist_add_recordingtitle' of git://github.com/Sophist-UK/picard into Sophist-UK-sophist_add_recordingtitle

Conflicts:
	NEWS.txt
Merge branch 'sophist_fix_plugin_install' of git://github.com/Sophist-UK/picard into Sophist-UK-sophist_fix_plugin_install

Conflicts:
	NEWS.txt
Make AcoustID use Recording IDs instead of Track IDs. (PICARD-526)
Merge branch 'sophist_fix_id3v23_date_yyyy-mm' of https://github.com/Sophist-UK/picard into mb-master
Merge branch 'master' of github.com:musicbrainz/picard into mb-master
Fix issue with date format yyyy-mm

MB sometimes gives dates in form yyyy-mm. Mutagen cannot save id3v23
dates in this format and truncates them to yyyy. Then they don't match
when the file is reloaded.

This fix detects New metadata dates in this format and truncates them.