default_storage-related cleanup.

Remove submodules
add errata sheet
switch to default_storage for all file IO
clean up requirements
remove PIL dependency
More errata.
closes #503
Converted weekly email stats to a Celery task. Fixes #479
Merge branch 'develop' of github.com:harvard-lil/perma into develop
remove test for vesting manager view
Merge branch 'develop' of github.com:harvard-lil/perma into develop
fixed test for permissions
Merge branch 'dev.default_storage' of https://github.com/jcushman/perma into jcushman-dev.default_storage
closes #517
Updated Vagrant install doc. Need to install dependencies first.
Needed to copy settings from example to my own instance for
Vagrant based install. Freshened up install instructions
Switched to use the built in Django timezone aware logic to display
times and dates in templates. fixes #514
Merge branch 'develop' of github.com:harvard-lil/perma into develop
Took another pass at displaying times in the user's local time using
the JS approach (get the user's TZ info from their browser and
adjust our UTC date using JS in the users browser at loadtime.)

Using the moment.js lib which seems to be well regarded.

fixes #514