collection.cgi: Added "meta graph" for "dns_qtype" and "dns_rcode".

collection.cgi: Added "meta graph" for "dns_qtype" and "dns_rcode".

This will merge all query types and return codes into a single graph each.

get_n_colors() has been taken from the version 3 script to get the colors for
the graphs. get_random_color() imho is not suitable for that purpose as it can
return colors that are hardly different - which would result in graphs that
are hard to read. get_n_colors() now returns a hash-ref suitable to be passed
to meta_graph_generic_stack().

Signed-off-by: Sebastian Harl <sh@tokkee.org>
Signed-off-by: Florian Forster <octo@huhu.verplant.org>