[Shotwell] Source code reorganization

[Jim Nelson]

One item that's been on my mind for a while and was discussed here
previously (
http://lists.yorba.org/pipermail/shotwell/2010-September/001088.html) is
reorganizing Shotwell's source code.  With whitespace and comments, Shotwell
is now over 70,000 lines of code.  The old model -- current before about an
hour ago -- was a flat list of files in a single directory with minimal use
of namespaces.  I've checked in to trunk a new model.

Rather than go on about it here, anyone interested should read a page I've
written about it on our architectural overview:
http://trac.yorba.org/wiki/ShotwellArchSourceOrganization

If you're currently working on a patch, you'll want to update your local
copy and merge with the new code before submitting.

Further work will follow to move more of the code into separate units and
further clean up the organization.  This is a first step toward a more
manageable code base.  Hopefully from here on it's smaller, more incremental
changes.

Cheers,

-- Jim