Store transform events and size in DB

[ponyisi]

Store the total_events and total_bytes fields in the database.

Right now the information will be updated on the completion of each file. I don't know if this is necessarily useful or if we should wait until transform completion, although updating as we go makes more sense from a user display point of view (if we update only at the end of the job we should probably hide the relevant fields from the user-facing page until the transform is done).

[gordonwatts]

I love this - I would approve it if I was reviewing it, but feels like something Ben should look at since the interactions might be subtle.