WIP: ActionEvents filter

Requesting comments, especially on tests.  This branch includes some commits which are waiting on PR 140 and 141 to land, but the API should not change.

I'm not positive this exercises all possible cases; I'm also planning to add a 1-2 second delay in the event consumer loop so we can test adding actions midflight.

All input welcome!
See, here we have taken the string entity.Tag, parsed it, confirmed it was a unit tag, and then thrown that information away in order to pass it through to this other function.  What you should do is have watchOneUnitActions accept a names.UnitTag, and not throw that information away.