Attempt to make code editor background image preloading more reliable
Attempt to make code editor background image preloading more reliable

https://github.com/codecombat/codecombat/commit/624e4f8b791162ad62d029b1bf4b846ac859bb11
  wasn't fully effective, so this adds some redundancy.

javatlacati/codecombat,codecombat/codecombat,javatlacati/codecombat,codecombat/codecombat,javatlacati/codecombat,codecombat/codecombat,javatlacati/codecombat,javatlacati/codecombat,codecombat/codecombat,codecombat/codecombat