Add model fields for video width and height

[crgwbr]

• Add width and height fields to the AbstractVideo model.
• Use ffprobe to populate these fields.

Builds on work in #126.

[seb-b]

@crgwbr can you give this a rebase and fix up the conflicts, I'll do a release with all the changes after reviewing this

[crgwbr]

Done—thank you 🙏