Treasure chest fixes, new foe and more!

I'm done with revamping the chest's physics and collision systems. This change took a lot of time and work and fumbling alone in the dark, but now the mechanics seem a bit more robust and predictable. 

Fixes :

-changed the way the chest behaves with turtles, to make it more consistent and deal with a lot of bugs

-reduced the stuttering when a turtle lifts the chest from under

-the chest is no longer pushed to the side when dropped from under a corner

Content changes : 

-changed the look of switches and switch blocks so that they feel more like walls and buttons, and less like dangers

-level design tweaks to Risky loop, Inky problem and Cosy courrier

New stuff : 

-added a new danger, big clams that clap on your face and also destroy the chest, although they aren't in any level yet

-added an appear/disappear animation for the gold star you can collect

There are a few bugs left from the new system, but they're due to pixel perfect split second interactions mostly, I will have to see if I take time to work on them. Right now, I want to get back to adding content.