DNX needs to inform users when servicing is not possible

[blowdart]

Currently nothing happens if the breadcrumb directory does not exist. This is a problem.

When XRE on Windows starts and cannot find the breadcrumb directory it needs to inform the user of this problem in a discoverable way.

And by discoverable I don't mean sending something to an ilogger (once it's moved downwards by #1118) in the vain hope that a listener has been configured, I'm meaning write to the console and the event log by default, with a way to disable in case it's on purpose.

[victorhurdugaci]

Moving this to 1.0.0 because by then we should have logging in XRE.

[muratg]

We plan to make servicing and security related work a "theme" in beta6.