Fixed some problems when we tried to deploy our instance

[pm5]

Two things fixed:

• Added Ubuntu APT key.
• Freezed django-celery-transactions at 0.1.2 which is the version celery-haystack wants.

[philipn]

Thanks so much!

Could you rebase and remove https://github.com/localwiki/localwiki-backend-server/pull/83/commits/7bb4bea1053076bab224b6579ba9efa6d27c382a from this PR?

[pm5]

No problem. My bad. Re-sent the pull request at #84.