Add macro removeentity_iter()

Also when we switch everything to not use 'active', we'll need this
macro to remove entities while iterating forwards through the vector one
at a time.

desktop_version/src/Entity.h

@@ -8,6 +8,8 @@
 #include <vector>
 #include <string>
 
+#define removeentity_iter(index) { obj.removeentity(index); index--; }
+
 enum
 {
     BLOCK = 0,