ng2.UISrefActive: Doesn't work when the UISref is on a different element

[christopherthielen]

See ui-router/quickstart-ng2#10

The bug is from how we access the UISref in the UISrefStatus: by injecting it into the constructor here: https://github.com/angular-ui/ui-router/blob/master/src/ng2/directives/uiSrefStatus.ts#L58

We should probably be using the ContentChild feature to find the child UISref(s): https://angular.io/docs/ts/latest/api/core/index/ContentChild-var.html