Redid set_video_id as data migration, using orm references, not imports

To address #1617. Not 100% sure it does what was wanted, but follows the logic of the old migration. No errors, just the following types of messages when running the migration:

```
DEBUG:kalite:Adding dubbed video map entry for ne (name=nepali)
DEBUG:kalite:Adding dubbed video map entry for en (name=english)
DEBUG:kalite:Adding dubbed video map entry for pnb (name=punjabi)
DEBUG:kalite:Adding dubbed video map entry for uk (name=ukranian)
DEBUG:kalite:Adding dubbed video map entry for el (name=greek)
DEBUG:kalite:Adding dubbed video map entry for pt (name=portugues)
DEBUG:kalite:Adding dubbed video map entry for id (name=bahasa indonesia)
DEBUG:kalite:Adding dubbed video map entry for es (name=espanol)
DEBUG:kalite:conflicting entry of dubbed_youtube_id XMCNLtPxRQk in el dubbed video map
DEBUG:kalite:conflicting entry of dubbed_youtube_id 7LNYIXoRCZg in el dubbed video map
DEBUG:kalite:conflicting entry of dubbed_youtube_id SOfgVnS6GSw in ar dubbed video map
DEBUG:kalite:conflicting entry of dubbed_youtube_id qCRZ3ijIx6k in ar dubbed video map
DEBUG:kalite:conflicting entry of dubbed_youtube_id PuX_UfgLJ18 in id dubbed video map
DEBUG:kalite:conflicting entry of dubbed_youtube_id HBt9DysNEDw in ru dubbed video map
```