Actions tab redux

The main goal of this MR is to make the tabbed UI in ddr-admin easier to understand and maintain. The actual appearance changes very little -- mainly just the styling of the "action" links that appear immediately below some tabs (e.g., "Edit"). Internally, there were many changes, but mostly to make certain things easier, like custom conditions and asynchronous loading. I am also motivated by a longer-term goal of expanding the publication workflow to include a "previewable" state, but that's not part of this MR.