merge Milestone easier buildout into develop

* refactor and split buildout files https://github.com/liqd/adhocracy/issues/138
* move adhocracy.buildout to the  adhocracy repro, move the adhocracy package to src/
... https://github.com/liqd/adhocracy/issues?milestone=4




Todo:

* make build.sh work again


@phihag  do you now how to make the history of moved files visible with github?