Add doc/openhmis.dia, a draft diagram of OpenHMIS.

This corresponds to the version posted in this message:

    From: Karl Fogel
    To: Dave Totten
    Cc: OpenHMIS Discuss
    Subject: Re: Finding entry points for new developers (for Eric & Saro).
    Date: Wed, 12 Nov 2014 14:13:37 -0600
    Message-ID: <87a93wdvny.fsf@ktab.red-bean.com>

    http://openhmis.pcni.org/developers/discussion-group?place=msg/openhmis-discuss/Iu2z0RMHJko/iH0IzuOM9L8J

    Same as:

    https://groups.google.com/a/openhmis.org/d/msg/openhmis-discuss/Iu2z0RMHJko/iH0IzuOM9L8J