Refactor to use Subscription objects
Provide each subscription with its own queue

--HG--
extra : amend_source : c13baa7418c3031d0ebbc66d4b64b9ac2fd4501a
Event queues now parse XML
Some pylint fixes
resolving merge conflicts
Merging with master
Small fixes
*%@^£&^ pylint
Using weakrefs for mapping
Allow for custom queues to be passed to subscribe
Prevent resubscription.
Allow access to an event's raw xml
Preparation for cache invalidation on events
updating requirements and tidying webapp
Reorganisation of event code + a test
Pylint doesn't know sphinx conventions- sigh
Merge pull request #130 from lawrenceakka/eventing-2

Eventing 2 - Further work