Redo the review request ID column to fix breakages.
The new registration system for datagrid columns in Djblets was

incompatible with the way that the review_id column works for the

dashboard. This column was being overwritten in __init__, which meant

that it skipped registration. The original column had no way of grabbing

the right field itself, resulting in a breakage.
The hack is now gone, and a dedicated column has been created for the

review request ID. I've also shortened the label and made it more clear

this is about review request IDs, not review IDs.

Added the column. No more crashes.