build: reduce Extra contents to bare minimum

Improve the build system, so that configuration files are installed
per tool basis. Also, introduce post_install targets, so that config
files can be altered in some way, e.g. done by trafgen. Moreover,
move custom targets from Extra to tool-specific Makefiles.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
build: Use -n option to head command

Make the call to `head' equivalent to the one to `tail'.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>