Patch "Push".2

Following things were added or changed:

• Fixed an unintended solution in a certain level which ignored half the objects involved.
• Tweaked "More Doors" to fit the intended difficulty level better (it should be harder).

I also started keeping track of level revisions this version, which altered the save structure. Due to the way I'm currently handling saved data, this means all progress could be reset (my apologies in advance!). This shouldn't happen anymore in the future (although I'm not sure yet if the data persists between different builds; it should but you can't ever be sure with WebGL). 

Moving forward, levels that have been revised in a significant way will have its "completed" status revoked. Considering all levels within a zone are unlocked by default, this shouldn't affect progress in a major way. Look at it like this: instead of having to "do a level again", you're really solving a different level, just with the same name!