Integrate additional scripts in pre-existing scripts

- swift-dul-daemon is now integrated in dul-daemon script
- swift-dul-initrepo is now integratetd in dulwich script
Remove default dependency to gevent

* Setup.py no longer install gevent and geventhttpclient as
* dependencies.
* Swift backend unittests are skipped if gevent and geventhttpclient are
  not installed.
* Greenthread unittests are skipped if gevent is not installed.