Add support and docs for adding columns to datagrids.

Review Request #5364 — Created Jan. 30, 2014 and submitted — Latest diff uploaded

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master

Reviewers

Add support and docs for adding columns to datagrids.

This brings over the new DataGridColumnsHook into the
reviewboard.extensions.hooks namespace, and introduces a specialization
for the dashboard called DashboardColumnsHook.

There's also docs covering how to use these new hooks, along with
examples.

Added a custom column to the dashboard.

Viewed the new doc pages. Didn't see anything immediately wrong.