Turned off DOM highlight noise after A/B test insignificantly showed it hurting.
Move sync pvp status UI to control bar

Replaces level name UI for hero-ladder levels.
Hide problem alert on code reload
Add problem range highlighting back

Now full line still pulses, and specific problem range has a darker red
background.
More reductions in memory usage for iPad.
Added stripe checkout script.
Merge branch 'master' of https://github.com/codecombat/codecombat
Merge branch 'master' into production