Migrate graphite_web to uwsgi

Overview:

* add uwsgi application container
* uwsgi ini configuration for graphite-web
* monit and upstart scripts for process monitoring
* modified start/stop scripts for uwsgi upstart job

Previously, graphite_web role was only compatible with Apache as there was no
nginx server block (analogous vhost) for the built-in graphite-web django
application.  These changes introduce uwsgi as the underlying application
container for graphite-web. These changes decouple graphite from Apache.

Note: The current Apache vhost should probably be rewritten to use a mod_uwsgi
proxy pass instead of the existing mod_wsgi configuration.

Addresses issue #253

/cc @tonycoco