Dispose of ASP.NET Core bits

[iantalarico]

Properly dispose of ASP.NET Core bits.

1. Services registered with HttpConfiguration that implement IDisposable are cleaned up automatically.
2. We dispose of CloudTrace via Event Handlers that are called during dispose.
3. Properly Dispose of the ErrorReportingExceptionFilter #803 To track proper disposal for ErrorReportingExceptionFilter.
4. Properly Dispose of all ASP.NET Core Middleware #802 To track proper disposal for ASP.NET Core Middleware.

[jskeet]

Makes sense in general - adding IDisposable increases the burden of using these classes of course, but it sounds like that's basically unavoidable :(

[iantalarico]

Thanks Jon