A note about logging configuration

[Tom Zeller]

> But I think we should just skip the idp.logDir thing and pass in idp.home
> by itself and not bother with the rest of the properties.

The above is what I have ready to commit, meaning inject the
ApplicationContext into the LLS via AppCtxAware and then set only the
'idp.home' property on the LoggerContext with a note in logback.xml
that only the ${idp.home} property is available.

Concerns ?