Global filters for $state.is() / $state.includes()

I keep running into people writing code like `ng-class="{active: currentState === 'foo.bar.baz'}`

It would be really cool if there were some filters provided to simplify this for people, and provided for more readable code, like `ng-class="{active: 'foo.bar.baz' | isCurrentState}` or something. (I realize fully well that linguistically, this looks weird --- but it's a bit clearer than the expression, IMO)

I'll take a few minutes today to write such filters, up to you whether you want to merge it, I suppose