Block neighbor detection improvements

[TheRealCatherine]

At least with the current physics system blocks need to know not only what blocks support them but also what blocks they support. This involves running 10 separate overlap spheres, 1 for each possible position, any time a block needs to update its cache. This can almost certainly be reduced to 2 carefully places spheres that only overlap with the self, above/below, left, right, back, and forward - probably by locating it around (-/+)0.7 with a size of 0.6

This may or mat not even be beneficial, it would take measuring to determine.