Re-added sprites to vivarium-web
Re-added sprites to vivarium-web

-TODO: web drawing is not correct. Fix this before refactoring swing/web
  to use the same logic and employ UI delegate objects.
-TODO: Figure out how to avoid replication of sprite files in the
  repository. GWT compiles require the resources to be at specific locations
  so this is non-obvious.

juckele/vivarium,juckele/vivarium,juckele/vivarium