[#1358] Fix auth error on datapusher_hook

When logged in as a non-sysadmin user, you always got an error like:

Process completed but unable to post to result_url

This was caused by calling task_status_update, which is sysadmin only on
datapusher_hook without ignore_auth in the context. We can safely add it
at this point because access has been already checked.

Added some tests.
[#1358] Show actual timestamp, translate string
[#1358] Make DataPusher statuses translatable
Merge branch 'master' into 1358-datastore-ui
[#1358] Tweak captions to make them clearer for users
[#1358] Change tab name
[#1358] The joys of PEP8
[#1358] Revert docs theme to the version on master
Merge pull request #1358 from okfn/1358-datastore-ui

New DataStore UI fixes and tweaks