IIS Service checks

How it works: 
- a sites ServiceUptime is reported as 0 if the site is not up, so we report it as down when we get a value of zero.
- if a site that we specified is not in the wni object, we report it as down: either it got deleted, or the IIS service as a whole is down.

@conorbranagan if you want to take a look.

Tested on windows 2012 for now
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