Upgrade to setuptools

* New installation procedure and folder structure:

  $ python setup.py install

  installs the 'harvestingkit' Python package. For example:

  >>> from harvestingkit import elsevier_package

* Updates all imports to use local imports.

* Now required config variables are optional:

  CFG_CONTRASTOUT_DOWNLOADDIR
  CFG_SPRINGER_DOWNLOADDIR
  CFG_OXFORD_DOWNLOADDIR

  will be installed under var/data/{elsevier,springer,oxford}
  unless overwritten in invenio-local.conf.

* For configs related to login information:

  springer_config.py
  oup_config.py

  is still required to be placed under 'invenio' root package
  path.

* Removes unrelated files and updates .gitignore.