Allow configuring what columns to display in commitfest page

[JelteF]

There are many columns that can be useful for filtering/sorting patches in particular ways on an ad-hoc basis. Showing all of that information all the time means the commitfest page becomes to cluttered. So we should have a way choose what columns to display on that page. This also gives more freedom to add new columns, because they don't clutter pages people that don't care about this information.

Once implement some future improvements could be to allow saving the default sorting/columns/etc in your profile or local storage.