Code review comment for lp://qastaging/~charlesk/indicator-datetime/lp-1295799-date-menuitem-should-open-calendar

Wow, simple changes cause a lot of ripple. We should probably long term think about a way to get the action names into consts so that we're not duplicating them all over the codebase. Then we could "C++ namespace" as well as "GAction namespace" them. Not for this MR though.