Mid-Jam Bugfix Update

Small bugfix update that should make the game a bit less unfair!

• Feature: you can now press space to save a block for later.
• Using alt+enter to toggle fullscreen doesn't trigger  the "press enter to play" on the titlescreen.
• Block types now have different chances to spawn, so you'll get more stone blocks (that doesn't move around) and bone blocks (automatically falls down to fill up gaps) and less ghost / zombie blocks.
• Moving blocks will now treat the falling block as an obstacle, so they won't move INTO the falling block occasionally and cause it to get stuck (leading to two overlapping blocks, which just looked ugly).
• Ghost / Skull shapes now are on a timer instead of being a random chance, and tetrominos are much more common.
• Game over check now uses the correct collision check function, which should prevent  some false positives. (Shouldn't make a big difference since you already KNOW you're screwed when you've got blocks stacked that high, but it's technically more fair now)