Moving exception handling from scrapers/tasks.py to scrapers/router.py

- Minor refactoring of router.resolve_and_scrape.
Catch exceptions that occur in resolve_scraper
Split error reporting into 'exception' and 'error_text' fields
Merge branch 'master' into scraperpanel
Added rescrape.json couchdb design doc

- temporary measure while we work out a good way to manage couchdb docs
- load into couch using: curl -X PUT http://localhost:5984/store/_design/rescrape -d @rescrape.json
rabbitmq at akorn@localhost, rather than akorn@127.0.0.1
Merge branch 'master' into scraperpanel

Bringing scraperpanel branch into line with module organisation in master
Fixing up module imports

- akorn.couch -> akorn.celery.couch
- akorn.local_settings -> akorn.celery.local_settings
ignore local_settings.py and celerybeat-schedule
updating couchdb design docs