This commit adds a new page (Save origin) in browse enabling users to:

  - submit software origins (git, hg, svn) to save into the archive

  - see the list of submitted save origin requests

Related T336
Related T1119

Add an admin interface in order to manage the save origin requests that
users can submit through the web api or from the archive website.

Administrators will be able to:

  - manage the origin urls whitelist and blacklist

  - accept or reject save origin requests in pending state

  - see the lists of accepted and rejected requests

  - check the status of accepted save requests once they have been
    processed

Related T336
Related T1120

This commit adds a new endpoint to the Software Heritage Web API in order
to offer users the possibility to submit software origins to save into
the archive.

The type of origins that can be currently saved are: git, hg and svn.
Submitted urls are first test again a blacklist/whitelist to determine
if they are authorized to be loaded or not. Unknown urls will be put
under pending state until a manual review is performed to determine if
they can be safely loaded or not.

Related T336
Related T1121

  - try to reencode from iso-8859-* to utf-8 only for content with mime
    type application/octet-stream

  - never reencode when requesting the raw bytes of a content

In order for swh-web to display correctly everywhere, Webpack generated
assets (js, css) now target more browsers as before.

Previous targeted browsers: http://browserl.ist/?q=defaults

Current targeted browsers: http://browserl.ist/?q=cover+99.5%25%2C+not+dead

When an invalid origin url is provided as query parameter of the
content, directory, release or revision view, add the raw object
browsing url in the generated 404 error message.

Remove top level guards in settings modules introduced in rDWAPPS0bc0934bca8ee36bcb1e2f8ef57c951fd5c6acca
needed at the time to fix Debian packaging.
After updating debian/rules by specifying the path of the tests to run,
there is no more side effects due to nose importing all swh-web modules
when searching for tests.

When the bytes of a content are missing in objstorage, display the main
browse interface instead of a plain 404 error page. The HTTP error report
is now displayed in the content box of the browse interface.
The error message for missing bytes has also been improved.

Closes T1130