Fix source playback in use_warc=True mode.
Merge pull request #518 from jcushman/dev.warc2

Fix source playback in use_warc=True mode.
Add custom server_error views so that we can send REQUEST_CONTEXT [and thus get STATIC_ROOT]
Make the <title> of the 500 error say '500' instead of '404'
Fix typo in urlconf for upload_link URL
Some celery config for wsgi.py
Add phantomjs file variants in lib/phantomjs to .gitignore
Generate zip file from assets and metadata when links are created
Include vested and darchived statuses in link status service
Add a link assets archive download service
Place datetime serialization in utils.py
Create a perma updater task + super basic/insecure endpoint
Datetime serialization bug
Deal with some type errors
Deal with some peculiarities of how Link objects are saved
Fix bug in link saving