[kernel] Move more from kutil to kernel

The moving of kernel-only code out of kutil continues. (See 042f061)
This commit moves the following:

- The heap allocator code
- memory.cpp/h which means:
  - letting string.h be the right header for memset and memcpy, still
    including an implementation of it for the kernel though, since
    we're not linking libc to the kernel
  - Changing calls to kalloc/kfree to new/delete in kutil containers
    that aren't going to be merged into the kernel
- Fixing a problem with stdalign.h from libc, which was causing issues
  for type_traits.

src/kernel/cpu.cpp

@@ -1,6 +1,6 @@
 #include <stdint.h>
 #include "kutil/assert.h"
-#include "kutil/memory.h"
+
 #include "cpu.h"
 #include "cpu/cpu_id.h"
 #include "device_manager.h"