merge Milestone easier buildout into develop

https://github.com/liqd/adhocracy/issues?milestone=4
https://github.com/liqd/adhocracy/issues/138

Todo:

* make build.sh work again
* update Readme, make clear how to install develop (sqlite) or productive (postgres backend)

@phihag  do you now how to make the history of moved files visible with github?