CMake: add rules for installing headers

libparameter abd libxmlserializer headers.

Concerning libparameter headers: only core headers (needed for the plugins) are
currently exported.  We'll need to export the client headers too, but we must
make a distiction between the two classes of headers.  Also, some currently
exported core headers might not be needed (some cleanup is needed).

Signed-off-by: David Wagner <david.wagner@intel.com>