Bugs squashed

First bugfix to fix a few things I could squash quickly!

• Annoying ceiling spike removed in the long sewer room
• Levels are preloaded now, should help a little bit with loading performance
• Wall spikes have about one pixel less hitbox since they seemed a little too sensitive before (Stalactites unchanged)

Bigger things I haven't got to yet:

• The blockchain puzzle is too glitchy. This will require some bigger physics changes
• Godot 3's 2D lighting system is known to get laggy in certain circumstances, especially with multiple lights and larger images. This is causing some of the bigger hiccups in-game. There are some potential workarounds but they are fairly involved.