Moved all Pyro-dependent modules from mdrunr to server.

"mdrunr.py" is now a 'backend', handling the queuing system, when to submit
jobs etc.

"server.py" is a module that wraps "mdrunr.Mdrunr" queues into Pyro
daemons to allow access from other processes.
Split mdclient into remote client and job definition sections.

"mdclient.py" contained utilities to connect to a Pyro queuing server,
and the class Mdjob which defines a job. This commit splits these
orthogonal activities. The Mdjob class is brought back to mdrunr, and
the utilities to connect to a queuing server are moved to a new
"client.py" file.
Updated "usage.md" to reflect changes in module structure.
Merge branch 'decouple_remote'
Basic "developper's documentation".

Added 'dev_docs.md', which provides a brief overview of the internals.
Started "docs" folder.

Re-grouped all the documentation into a single folder.