Archiving

This is a big branch (and it might be nice to squash the commits before committing to master).

This adds automatic archiving of artifacts triggered by pulling the artifact details from Jenkins.

capomastro/settings.py adds...

from archives.tasks import process_build_artifacts
POST_BUILD_TASKS=[process_build_artifacts]

POST_BUILD_TASKS are chained from the task that downloads the details of the newly-completed build.

These are put into an "archive" defined as the "default" archive (see admin) the admin will only allow one archive to be the default.