Check if EMBEDLY_KEY has been set

This will check if EMBEDLY_KEY has been set in settings. If not
it will return a nice error message instead of throwing a 500
error.
Modified embeds.py to make it work

The Embedly API was not working at all because the return
value of Embedly (client) offered the attributes in dictionary
style and not as an object. Now everything seems to be fine.
Handle SQLite substr syntax

Addresses https://github.com/torchbox/wagtail/issues/11
Added multi-backend support into wagtail search. Added Database search backend
Merge branch 'master' of github.com:torchbox/wagtail
Search: Updated search handlers and tests to use get_search_backend
Search DB Backend: Don't ignore the fields parameter
Merge remote-tracking branch 'upstream/master'
output template errors on preview into the preview window - fixes #2
Search: Unit tests
Search: Fixed issue with query string normalisation not removing double spaces
More unit tests
Merge branch 'master' of https://github.com/spapas/wagtail into spapas-master
Search: Various tweaks to backend importer
Search: more unit tests
update_index command is now callable from unit tests
DB backend now doesnt attempt to search on callable fields
More improvements to unit tests
Modified tasks.py to use celery only if available

Please see the comments inside tasks.py.
TL;DR: Defines a fake "task" decorator - the fake
decorator was needed to add the delay() attribute
to the send_notification function
Added multi backend support into searcher