Updating installation docs

When following the installation docs there is a missing requirement of ceres.
Add installable wsgi file

This simplifies the graphite.wsgi configuration example.

When running graphite in a virtualenv with gunicorn, this also allows running
`gunicorn graphite.wsgi` directly, without any additional configuration.
STORE as a dynamic backend
Isolate default store params in its module
Load backend from environment variable if present
remove sys.path hack, manage.py one level up
Add cyanite store backend
Hook into the finders API instead of replacing the store
Cyanite isn't in stock graphite
re-add the possibility to configure hosts
Move match_entries out of finders to avoid ceres dependency
Move cyanite out of the graphite namespace
Undo manage.py change, other branch already dealing with that
Spare a couple of lines, add missing import
Updating install documentation for ceres.

There currently is no formal ceres release, therefore there is no direct pip install.
It must be install via github (for the time being)
Merge remote-tracking branch 'upstream/master' into feature/store-backend
Improve way to catch / throw exceptions
Cleanup, mostly missing imports
Split ceres and whisper finders
Add simple test for a custom finder