First working, not-tested, version of a multi-journal SciPost.
Will rebuild all views to CBVs to use mixing for the recurring
`journal` context variable.

The settings environment has been changed to the preferable
 situation in which secrets are kept secret, but all settings
 are still tracked, even local settings. Use the updated readme
 file to get started again. Please track your settings, unless
 the settings really are secret!

The url is based off of the DOI. Because the DOI is always the same,
making more than one factory instance crashes the detail page.

UnpublishedVettedCommentaryFactory does not have this problem,
as it has an empty DOI field and a valid (random) arxiv identifier.

CAUTION! READ ME!
This migration will setup a proper attachment environment.
This means, that for existing files (journal publication!),
 these folders/files should be completely moved to the MEDIA_ROOT
 folder, else this will return a 404 NotFound for the related
 files.

The `static` folder will be ignored in the future commits. All
 existing files in this folder in the repository are now removed.

The README.md file is updated to include a correct workflow
 on how to deal with static files.

Added a NPM packages.json list which manages
 JavaScript packages. Most important packages added
 is the Webpack package which acts as an assets
 bundler.
It is added in its most basic working form. This
 includes additional settings in `settings.py`
 and the template tags in `base.html`.
Please read the updated Readme.md to easily get
 started using Webpack for your new assets.

The acknowledgement message is no longer hardcoded in
theses/views.py, but resides in the top-level strings module.

New Group defined: Developers.

New Permission: can_view_docs_scipost (necessary to view the /docs/).

Need to run the add_groups_and_permissions management command.