[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/page_tree.cpp

@@ -1,5 +1,7 @@
+#include <string.h>
+
 #include "kutil/assert.h"
-#include "kutil/memory.h"
+
 #include "frame_allocator.h"
 #include "kernel_memory.h"
 #include "page_tree.h"
@@ -33,7 +35,7 @@ page_tree::page_tree(uint64_t base, uint8_t level) :
     m_base {base & level_mask(level)},
     m_level {level}
 {
-    kutil::memset(m_entries, 0, sizeof(m_entries));
+    memset(m_entries, 0, sizeof(m_entries));
 }
 
 page_tree::~page_tree()