closes T800

enable to specify ISO date string as parameter of some endpoints of the swh web browse application (as in the web api)

closes T810

first pass on improving and completing the sphinx documentation for swh-web: reorganize rst files, start documenting the swh web api urls, add example links for swh web browse, ...

this is far to be complete and shiny at that point but it's a good start

  - move django settings for tests in new swh.web.settings.tests module
  - set DJANGO_SETTINGS_MODULE environment variable value to that module in debian/rules

closes T806

note: this was enabled only for swh-web, but it really needs to also be in
swh-docs, because we pull there docs from individual modules

closes T786

factorize some code with swh api regarding the url patterns declaration

add non-minified version of highlightjs and its line numbers plugin for reproducibility and editability purposes

centralize documentation of browse uri scheme in a dedicated section of sphinx doc instead of putting it in view docstrings

use correct package name on PyPi for the magic module and ensure support for old and recent version of its api