Add functionality for whitelisting single addresses or network ranges.

Add functionality for whitelisting single addresses or network ranges.

This commit adds the posibilty for generating a ignore list based on a
set of IP addresses or networks (IPv4/IPv6 are supported) which are provided
by an so called ignore file.

The path and the filename can be configured by using the "IgnoreFile = /path/to/somefile"
option inside the config file of guardian. Using this feature is completely optional and
only be activated if an ignore file has been specified.

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