fix(dashboard): support the nodecg-dialog attribute within shadow roots (#384)
fix(dashboard): support the nodecg-dialog attribute within shadow roots (#384)

Before this, elements inside of shadow roots (i.e., Polymer elements) with the `nodecg-dialog` attribute would not open dialogs.

See https://www.polymer-project.org/2.0/docs/devguide/events#retargeting
nodecg/nodecg,nodecg/nodecg,nodecg/nodecg