Prevent overlay-icons from being inserted multiple times on interval
Prevent overlay-icons from being inserted multiple times on interval

- our checkForEmbeds methods in overlay-icon.js wasn't checking for
existance of the overlay icon before appending it. So we we're adding
multiple copies of the icon into the dom on an interval.

- fixes #223
- refs #224 surely this was affecting performance

meandavejustice/min-vid,meandavejustice/min-vid,meandavejustice/min-vid