Fixes name of alchemy_preview_mode_code helper
Fixes name of alchemy_preview_mode_code helper

In 40cec4cfb00150125047b08f56462fbcd64ded51 we accidentally renamed the `alchemy_preview_mode_code` helper into `preview_mode_code`.

mixandgo/alchemy_cms,IngoAlbers/alchemy_cms,nielspetersen/alchemy_cms,mtomov/alchemy_cms,chalmagean/alchemy_cms,akra/alchemy_cms,mamhoff/alchemy_cms,mtomov/alchemy_cms,mamhoff/alchemy_cms,AlchemyCMS/alchemy_cms,mixandgo/alchemy_cms,mtomov/alchemy_cms,nielspetersen/alchemy_cms,IngoAlbers/alchemy_cms,mixandgo/alchemy_cms,akra/alchemy_cms,chalmagean/alchemy_cms,mtomov/alchemy_cms,AlchemyCMS/alchemy_cms,IngoAlbers/alchemy_cms,mixandgo/alchemy_cms,nielspetersen/alchemy_cms,robinboening/alchemy_cms,akra/alchemy_cms,akra/alchemy_cms,IngoAlbers/alchemy_cms,robinboening/alchemy_cms,chalmagean/alchemy_cms,chalmagean/alchemy_cms,robinboening/alchemy_cms,AlchemyCMS/alchemy_cms,nielspetersen/alchemy_cms,mamhoff/alchemy_cms