v1.16.0

@esri/arcgis-rest-items

• New Features
  • new getItemGroups() method c0cd950
  • new removeFolder() method b915ecb

@esri/arcgis-rest-request

• Fixes
  • dont misinterpret custom referer headers as request parameters 4ff33b1
  • dont set referer headers to null in browser apps 0b1bf2b