configure NullHandlers in case logging is not requested

We frequently see error messages of the form:

[Tue Nov 12 01:06:53 2013] [error] No handlers could be found for logger "cache"

This commit fixes that issue.
reconfigure the metricAccessHandler

Make it have a backup of 1 file, like all the other Rotators. Also, this logger
isn't even used anywhere, so it will not matter.
introduce a function to configure loggers
configure infoLogger via function
configure exceptionLogger via function
configure cacheLogger via function
configure renderingLogger metricAccessLogger via function
make log rotation configurabel
fix import
midnight should be a string
adding test file for logger
improve tests

Test various aspects of the logger module.
add docstrings to the unit-tests
update comment
check that deactivation of log file rotation works
adding tox testing for python2.6 and python 2.7
fixup NullHandler for python2.6