splango.models.Goal: added get_records_count_per_variant
splango.models.Enrollment: added TODO
`experiment` should be removed as an attribute
splango.models.Variant: added get_goal_records()
splango.views: added experiment_goal_report
and its url declaration
added template for splango.views.experiment_goal_report
Merge branch 'master' of github.com:lookup/Splango