tomahawk: Update to bugfix release 0.8.2.

Fixes a few annoying bugs (in my case it's the painting issue that's
most annoying):

 * Show error message if saving tags failed.
 * Fixed painting issue on search page.
 * (OS X & Windows) Fixed crash during collection scan.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
tomahawk: Fix finding Phonon VLC backend.

Using propagatedBuildInputs only works for environment.systemPackages
but not for using nix-env, because on NixOS we already have a default
QT_PLUGIN_PATH set there.

The main reason why I'm using the VLC backend and not providing options
for other Phonon backends is because it's recommended upstream and also
will be directly used (via libvlc) in the upcoming 0.9 release.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>