Add Banshee.WebBrowser and Banshee.AmazonMp3.Store

This is a big commit that introduces two to-die-for features into
Banshee. First is a generic GTK WebKit-based embedded browser, called
OssiferWebView, which extends WebKitWebView. OssiferWebView is written
in C, because it makes fairly heavy use of WebKit and Soup APIs, for
which the C# bindings are rather lacking. A simple, easy-to-bind API is
exposed. In C#, Banshee.WebBrowser.OssiferWebView is available for
extensions to use for embedding a reliable web browser.

GTK WebKit 1.2.0+ is required. Fortunately, this is very easy to build
on openSUSE 11.2-era systems.

What is most important though, is the introduction of the
Banshee.AmazonMp3.Store extension, which leverages
Banshee.WebBrowser.OssiferWebView to provide an integrated and dedicated
Amazon MP3 store browser. Music can be browsed, searched, and purchased
in Banshee just as you would through Amazon MP3's web site in your
regular browser, however there are two (current) user experience
improvements:

  1. A cookie is always set by Banshee that tells the Amazon MP3 web
  site that a valid Amazon MP3 downloader is installed, thus avoiding
  nagging messages about downloading the installer (which notoriously
  does not work on Linux systems); and

  2. Mime-type hooks ensure that when audio/x-amzxml content is
  delivered by Amazon, that it is downloaded and immediately imported by
  the Banshee.AmazonMp3.AmazonMp3DownloaderService. The result being
  that as soon as a purchase is made, the purchase begins downloading
  and importing into your Banshee library automatically.

Further browser improvements and polish will be on the way:

  1. Basic back/forward navigation
  2. Searching from within the regular Banshee UI
  3. Ability to log out from within the regular Banshee UI
  4. Lots of other stuff I haven't thought of

I'm not as think as you drunk I am, Ossifer!