Add ability to switch video modes from the system menu.

I had to change PhysicalPage around a bit for this. Physical pages can now
be instantiated for any arbitrary physical address without worrying that
such pages end up in the kernel page allocator when released.

Most of the pieces were already in place, I just glued everything together.

LibC/stdlib.cpp

@@ -50,7 +50,7 @@ void* malloc(size_t size)
     size_t real_size = size + sizeof(MallocHeader) + sizeof(MallocFooter);
 
     if (s_malloc_sum_free < real_size) {
-        fprintf(stderr, "malloc(): Out of memory\ns_malloc_sum_free=%u, real_size=%x\n", s_malloc_sum_free, real_size);
+        fprintf(stderr, "malloc(): Out of memory\ns_malloc_sum_free=%u, real_size=%u\n", s_malloc_sum_free, real_size);
         assert(false);
     }