factored count_histogram out

port and address histograms now do their own rendering so they can
make intelligent decisions about their content rather than squashing
everything into strings
quick_config arguments now const refs

I missed that the quick config methods of the address and port histograms
were pass by value and the arguments weren't const.  Quick fix.
port histogram now gets colors from report

Port histogram queries a database in its respective report to find out
how to color itself.  This makes it an implicit legend.

time_histogram will do this too later
Merge branch 'working'

Conflicts:
	src/Makefile.am
	src/netviz/address_histogram.cpp
iptree::addr_elem now uses str() instead of <<