Added Stats.AggregateInGallery job. Need to be tested
1) Fixed AggregateStats program
2) And, moved the EventSource to the JobBase such that Enableevents can
be moved to the common JobBase class
Merge branch 'master' of https://github.com/NuGet/NuGet.WebJobs

Conflicts:
	src/Stats.AggregateInGallery/Stats.AggregateInGallery.Job.cs
	src/Stats.AggregateInGallery/Stats.AggregateInGallery.Program.cs
	src/Stats.AggregateInGallery/Stats.AggregateInGallery.csproj