Add Album Artist Website plugin - see PICARD-26

Adds a plugin to get the artist homepage MB relationship and insert into
website (ID3 WOAR tag).

Note: I used this plugin as a trial for using a Picard xml module to
handle MB WS2 xml response. See PICARD-581.
Add NEWS.txt
Remove unneeded imports
Handle album finalisation correctly.
Merge branch 'sophist_add_album_artist_website_plugin' of git://github.com/Sophist-UK/picard into Sophist-UK-sophist_add_album_artist_website_plugin

Conflicts:
	NEWS.txt
Merge branch 'Sophist-UK-sophist_add_album_artist_website_plugin'