Related T1768

these constants should be set in the SWH_CONFIG_FILENAME at deployment,
they have no reason to live in the code.

this is needed so we can spawn a production-like webapp (in docker)
without a memcache (makes documentation writing easier).

'revision log' endpoints with complex lookups are excluded
from this commit, as it's impossible to get a non-ambiguous URL
for them without excessive hacks.

Related T1768

It makes debugging easier.

swh-sidebar-collapsed value in localStorage due to other tests fails these tests.

It exist cases where file badly detected input encoding as ascii which results
in display errors in browse.

api-stat-counter was renamed to api-1-stat-counter, that resulted an error on api_stat_counter() call

Related T1768

So they don't clash when we start adding a v2.

So the inner function's module and name are shown by the 'show_urls'
command of 'django_extensions'.

It's more pythonic/idiomatic and consistent with what DRF does.