Add support for toggling notifications for nagios by servicegroups

[dlobue]

Support toggling alerts by nagios servicegroups as well as hostgroups. Also updated log messages to indicate whether alerts are being disabled for a servicegroup or hostgroup.

Lastly updated comments to reflect that host notifications are NOT disabled along with service notifications.

[dlobue]

Added it to the file comment.

[bison]

In addition to a comment linking to the Nagios source, why not define constants for these magic numbers that correspond at least roughly to the ones Nagios defines.

[dlobue]

@bison because there's over a hundred of them, we're only using 4, and I'm kinda going for MVP as I'm under a deadline.

[robert-chiniquy]

Does sound like a good idea for another PR though (or at least an issue opened to track that idea)

[lakshmi-kannan]

I wish we could have test cases. We'll need to have a mock nagios service I guess.

Code LGTM. +1.

[dlobue]

works in staging.