experimental “wardrobe” and “jukebox” reporters in dev mode

tentative preparations for first-class costumes and sounds
display costume thumbnails in speech/thought/value bubbles and watcher cells
let “switch to costume” block accept actual costume objects (in addition to names and numbers)
Merge branch 'master' of git://github.com/jmoenig/Snap--Build-Your-Own-Blocks

* 'master' of git://github.com/jmoenig/Snap--Build-Your-Own-Blocks:
  let “switch to costume” block accept actual costume objects (in addition to names and numbers)
  display costume thumbnails in speech/thought/value bubbles and watcher cells
  experimental “wardrobe” and “jukebox” reporters in dev mode