Move icons back into SIG data

static/apidocs/openapi.yml

@@ -1505,6 +1505,10 @@ components:
             Regex that matches this SIG's reference IDs. Generally for Spothole's own internal use,
             clients probably won't need this.
           example: "[A-Z]{2}\\-\\d+"
+        icon:
+          type: string
+          description: Icon from the Font Awesome set that represents this SIG, for use in the front end.
+          example: "fa-tree"
 
     SolarConditions:
       type: object