Get a single custom icon on a board.
curl -X GET \ https://myaccount.leankit.com/io/board/10113014456/customIcon/10113014778 \ -H 'Authorization: Basic base64encodedauthhere'
200 Success
{ "id": "10113014777", "name": "API Testing", "policy": null, "iconPath": "/customicons/24/212121/someIcon.png", "iconColor": "212121", "iconName": "someIcon" }