Introduce ILoggerFactory, IConfigurableLogger and a non-final LoggerFactory

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Following the discussion at google code:
https://plus.google.com/u/0/109021309194427511764/posts/DcN5GWWHnYt

we need a ILoggerFactory and consequently a IConfigurableLogger(?) interface 
for proper abstraction and maybe a LoggerFactory that can be extended to be 
ideally suitable for Dependency injection.

Original issue reported on code.google.com by martin.h...@gmail.com on 15 Nov 2011 at 1:24