Convert to 3.0 (git) source format

[yarikoptic]

It would be infeasible to create a .dsc otherwise without heavy manual filtering and splitting into multiple git repositories etc. Using 3.0 (git), which was used successfully (awhile back though) for few packages (pymvpa2-tutorialdata, sri24-atlas) we can create concise .dsc while keeping all the history and access to all the heavy files (under annex)