Branches view: show checkbox before branch/tag grouping nodes

Each individual branch has a checkbox in the Branches window that governs whether is is shown in the graph view.

When multiple branches are folded under a single entry in the (eg kokua has within it kokua/branch1, kokua/branch2, kokua/branch3 and so on) there isn't an easy way to show/hide all of the entries under there.

Right clicking produces a menu which includes Toggle, however that doesn't operate on the contents (I've bug reported that). The actual feature request here is to add a checkbox on the top level kokua entry so that show/hide can be done with just clicks and not needing to menu or click-hit space each time.