* Add costume dataURI to costumes from storage
Towards #515, LLK/scratch-gui#279
* Fix tests
* Load costumes incrementally
Some of our tests assume that at least some of our costume data is available before the costume data is loaded. So, provide as much costume data as is available.
* Remove unnecessary filter for null costumes
Resolved when we updated to load costumes incrementally.
/ht @cwillisf