"Master" branch should, in the UI, indicate that Master is a conceit of the UI

[pgunn]

Right now the WebUI pretends that any node in a repo that doesn't belong to a branch ("Branch": "") to belong to a Master branch. It'd be good to somehow indicate in the UI (perhaps put the word in parentheses) to indicate that that's not a real branch and that "UUID:Master" will not resolve as a node identifier.