De-duplicate entity collision checks for player/SCM

The entity collision check routine has been factored out into its own
function, so it no longer needs to be copy-pasted for the supercrewmate.

desktop_version/src/Entity.h

@@ -158,6 +158,8 @@ public:
 
     void entitycollisioncheck();
 
+    void collisioncheck(int i, int j, bool scm = false);
+
 
     std::vector<entclass> entities;