Treat times as UTC

This is not actually accurate but it makes live a lot simpler down the
line.

See https://www.pivotaltracker.com/story/show/62779118 for details.

This commit also changes the `data_id` function to not include the
dimension values as part of the id. This is because they are not passed
through to backdrop and therefore can't be used to rebuild the id at a
later stage if needed. Also, records are never identified by their
dimension values within a single bucked (they would be in separate
buckets).
Switching to latest version of backdrop-collector

The latest version of backdrop-collector has an extra parameter in set_up_logging() which allows one to specify the logfile_path. Previously logfiles were being created in a place relative to cron's working directory.
Merge pull request #17 from alphagov/upgrade-logging

Switching to latest version of backdrop-collector
Merge pull request #16 from alphagov/fix-ga-bucket-timezones

Treat times as UTC
Run travis on master
Break up the line so that pep-8 passes
Merge pull request #19 from alphagov/run-travis-on-master

Run travis on master
Merge pull request #20 from alphagov/pep8-fix

Break up the line so that pep-8 passes