Removed BBox, renamed position to origin

I've replaced the BBox class with a pair of inline functions in
check_bounds.hpp. I've also renamed the 'position' variable to 'origin' in
several locations.

These changes are mostly to alleviate ambiguity.

common/utilities/vector2.hpp

@@ -42,12 +42,6 @@ public:
 		return x*x+y*y;
 	}
 
-	double operator[](size_t i) {
-		if (i >= 2)
-			throw(std::domain_error("Out of range"));
-		return *(&x+i);
-	}
-
 	//Arithmetic operators
 	Vector2 operator+(Vector2 v) const {
 		Vector2 ret;