Logger refactoring

[glennc]

@pakrym is spiking it now, we hope to resolve some of the deficiencies in preview1.

Impacted issues:
#620
#618
#613

#534
#525

[cwe1ss]

Also related: aspnet/Hosting#1071

Looking forward to see what you come up with! 👍

[glennc]

We have an idea, but we decided it would be easier to discuss with code rather than write it all up first. Our backup plan is to just revert everything and go back to the way it was :).

[DamianEdwards]

@pakrym this is done now too?