Add support for dead task detection and auto restart

[haacked]

If a task gets in a state where it's marked as active, but nothing is working on it, it'll effectively block anyone from working on it.

We need to detect this case and log an error. Also consider auto restarting such tasks based on past average task elapsed times.

[odinserj]

This is a major problem for performing long-running tasks in ASP.NET app with WebBackgrounder, because it will be killed on AppDomain unload after the ShutdownTimeout of the hosting environment expiration (defaults to 30 seconds).

If you want to handle long-running jobs in ASP.NET application without using Windows service, take a look at http://hangfire.io (it is open-source, https://github.com/odinserj/HangFire).