Added bulk download, closes #123
Merge branch 'flask-rewrite' of https://github.com/jacksingleton/securedrop into jacksingleton-flask-rewrite

Conflicts:
	modules/deaddrop/files/deaddrop/test.py

This pull requests adds a "tmp" directory alongside "store" and "keys" to store
zip files built for bulk downloads. I've added an entry to the example_config
- existing users and developers will have to copy this to their config.py.