Allow including additional ignore files.

This commit adds the ability to specify additinal files
in the include file which should be included. Any containing
IP-addresses of those files also will be added to the hash
of ignored IP-addresses.

To include a file, just add "Include_File = /file/to/be/included" to
the ignore file. There is no limitation for number of included files.

This feature can be used, to include system specific files which contains
IP-addresses which also should be added to the ignore list.

Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>