From this moment on, we embed a fork of u1db called l2db.

this is part of a process to make the setup of the development mode less
troublesome. from now on, setting up a virtualenv in pure development
mode will be as easy as telling pip to just install the external dependencies::

  pip install -r pkg/requirements.pip

and traversing all the leap repos for the needed leap dependencies doing::

  python setup.py develop

- Related: #7288

In the past, we wanted dependency on leap.common to be optional, but now
because of the explicit use of the config path prefix and signaling, we want
to enforce dependency on leap.common.

It looks like it is no longer needed, but leaving it commented
until we do some more tests.

* add versioneer (patched for our particular repo config)
* add parse_requirements to unify requirement handling