The natpmp CMake build has no installation specified, so currently
we use the root source directory which contains the header files as
an include path in the daemon build. This may cause issues as case
insensative header includes for the standard library <version> will
incorrectly load natpmp's 'VERSION' file.

This patch copies the project's headers to an include directory
post-build, and adjusts the daemon's include path.

Change-Id: I4b318fb0309c72b94f4ea4e757035780ee2a8a63