Convert from CGI to WSGI

Instead of making admin.py and new_planet.py CGI scripts, set up a WSGI
handler (wsgi.py) and make that forward requests to admin.py and new_planet.py.
Although the added performance benefits of WSGI are not important for the
application, using WSGI results in more flexible deployment.
Stop using global objects to accumulate error messages

Since with the switch to WSGI, processes can persist and be shared between
requests, we can't use global variables for state - pass around error
message objects instead of using global objects.
fixup! Convert from CGI to WSGI
fixup! Stop using global objects to accumulate error messages
Serve all content, even static content from a single WSGI handler

OpenShift, which we want to be able to deploy onto, is very limited in
it's handling of static content - only URLs that start with static/ can
be served statically. We can eventually migrate images, css, etc, there,
but for now, just serve static cotent directly out of the WSGI handler.

At a minimum, we should improve this by adding handling for If-Modified /
If-Match and/or by adding an expiration time.
Add setup.py and requirements.txt

Add information about the application needed for automatic
installation of dependencies.