lp:1206147, website

Fixes https://bugs.launchpad.net/mixxx/+bug/1206147 ( http://www.mixxx.org/get-involved/ is still pointing to bzr).

The development circle depicted on the web site possibly needs an update following the git workflow though. This can be done easily with Inkscape using the new vector template.

Note: Imho the website and manual branches are core assets and should be available directly @mixxxx , not @mixxxcommunity.