- bug fix for SampleFrom (now work even if you check the json first)
- bug fix for dropdowns (now have an initial blank default option)
- feature additions for resources: in addition to using strings or `SampleFrom`, you can make `Resource` objects which take the filename of the resource and the following optional arguments: `required` (cannot choose an option or advance until the audio or video has finished playing), `autoplay` (plays when it displays), `controls` (show or hide controls).