Add allow_empty_insert to the InsertToMysqlVideo* tasks
Add allow_empty_insert to the InsertToMysqlVideo* tasks

because some deployments don't use video in their courses, or have quiet
days when no one watches a video.

* boolean parameter (default False)
* configurable from the [videos] section in override.cfg

Stanford-Online/edx-analytics-pipeline,edx/edx-analytics-pipeline,Stanford-Online/edx-analytics-pipeline,edx/edx-analytics-pipeline,edx/edx-analytics-pipeline,Stanford-Online/edx-analytics-pipeline