Pass class paramters to the debian class instead of perverting scope

At the same time, fix icinga-specific stuff in the debian class by
stopping the use of the global variable $nagios_use_icinga
Lint all files
Add upgrade notice about nagios::nsca::server

Move upgrade notes above Overview section to make them more obvious
require main package to be installed before all config files

Not having those files generates lots of errors. Among those are some
such as:

err: /Stage[main]/Nagios::Base/File[nagios_confd]/ensure: change from
absent to directory failed: Could not set 'directory on ensure: Could
not find group nagios at /etc/puppet/modules/nagios/manifests/base.pp:83

but other problems arise when trying to place config files when the
configuration directory doesn't even exist. As a side effect to this,
after the first puppet run, nagios doesn't start up since some config
files might be missing.

All of the config files have links like "notify => Service['nagios']"
and one would think that this would define the correct dependency order,
but apparently it does not.
main icinga config file is named icinga.cfg, not nagios.cfg
main configuration points to files in /etc/nagios3

is that really necessary? we're gonna need an icinga-specific config
file anyway from the looks of things.