Billing record have an optional video, so is not deleted if video is deleted
Added migration for billing record having optional video
Do not delete billingrecord if subtitles are deleted
Billing reports can now display billing records whose video was deleted
One more fix for billing reports with deleted videos
Improve display of billing records with deleted videos
add a deleted video billing test
Merge pull request #1551 from pculture/gh-1539

Gh 1539