add. Method get_latest_cohort_id.
rm. ref to 'MEDIAWIKI_DB_INSTANCE' in favour of cohort meta instance from settings.
add. Method generate_test_cohort to help with building test cohorts from other projects.
mod. Make _format_mediawiki_timestamp a class method.
add. Method generate_test_cohort_name to generate a formatted test cohort name.
add. Write to usertags[_meta] tables after generating test cohort.
mod. Updated settings vars.
mod. logging. move query defs out of methods (to be moved out of module).
add/mod. delete_usertags and delete_usertags_meta methods.  pep8.
Merge pull request #3 from rfaulkner/master

Update to user_metrics/metrics/users module to generate test cohorts by project.